Communication
`
`THE JOURNAL
`OF BIOLOGICAL CHEMBIXY
`Vol. 269, No. 9, Issue of March 4, pp. 6276-6278.1994
`0 1994 by The American Society for Biochemistry and Molecular Biology, Inc.
`Printed in U S A
`
`Structure-Activity Studies of
`Glucagon-like Peptide-l*
`
`illustrated in Fig. 1. In spite of the high homology, none of the
`other peptides tested show any affinity for the cloned GLP-1
`receptor (17) except glucagon which, however, has an affinity of
`at least a factor of lo4 less than GLP-1. Surprisingly, Exen-
`(Received for publication, November 15, 1993, and in revised
`din-4, a 39-amino acid peptide from Helodermantidae venom,
`form, December 9, 1993)
`which also shares a high degree of homology to GLP-1 (Fig. l),
`has recently been shown to be a very potent agonist of GLP-1
`Kim Adelhorst, Brit B. Hedegaard,
`while Exendin-4-(9-39)-amide was found to be a n antagonist of
`Liselotte B. Knudsen, and Ole Kirks
`GLP-1 (18, 19).
`From Diabetes Discovery, Novo Nordisk AIS, Novo All&,
`So far, very few studies have been performed to investigate
`DK-2880 Bagsvaerd, Denmark
`the structure-activity relationship of GLP-1. Studies have been
`A series of analogs of glucagon-like peptide-1 (GLP-1)
`performed primarily with N- and C-terminally extended or
`was made replacing each amino acid with L-alanine to
`truncated analogs (20-25). These studies have indicated that
`identify side-chain functional groups required for inter-
`the N-terminal histidine is very important for receptor affinity
`action with the GLP-1 receptor. In the case of L-alanine
`and that N-terminally extended forms of GLP-1 have limited
`being the parent amino acid, substitution was made
`activity only. The C-terminal part of the molecule also seems to
`with the amino acid found in the corresponding position
`be important for the action of GLP-1, although not as critical as
`in glucagon. Binding assays were performed using the
`the N-terminal histidine. GLP-1-(7-34) and GLP-14735) ex-
`cloned rat GLP-1 receptor, and receptor activation was
`hibit a somewhat reduced receptor affinity while GLP-1-(7-33),
`monitored using RIN 2A18 plasma membranes. The ana-
`GLP-1-(7-22), and GLP-1-(7-20) show no biological activity.
`logs that showed the weakest receptor binding were
`fur-
`The glycine-extended form of the peptide, GLP-1-(7-37), has
`ther compared with native GLP-1 by circular dichroism
`identical efficacy compared with GLP-l-(7-36)-amide. Further-
`spectroscopy to investigate possible conformational
`more, Exendin-4, having a 9-residue C-terminal extension, is a
`changes. We conclude that the side chains in positions
`7,
`very potent GLP-1 agonist (19, 24). Some analogs have been
`10, 12, 13, and 15 are directly involved in the receptor
`made where the specific residues in positions 10, 15, 16, 17, 18,
`interaction while positions 28 and 29 are important for
`GLP-1 to adapt the conformation recognized by the re-
`21, 27, and 31 were exchanged to the residues found in GRF.
`ceptor.
`This study indicated the residues in positions 10, 15, and 17 to
`be most important for the effect of GLP-1 (23).
`As indicated above, the structure-activity studies performed
`so far have pointed at both the N- and C-terminal part of the
`Glucagon-like peptide-1-(7-36)-amide (GLP-1)’ is formed by
`GLP-1 molecule being involved in the receptor interaction.
`post-translational processing of the proglucagon precursor pep-
`However, no study has been performed in order to investigate
`tide (1-5). The peptide is secreted from the distal gut into the
`the function and importance of each amino acid in the peptide.
`circulation after the ingestion of, for example, a carbohydrate-
`To address this question, we now report on the systematic
`rich meal. The peptide has several effects on the endocrine
`exchange of each amino acid in the sequence of GLP-1 by L-
`pancreas. It stimulates insulin
`secretion in the presence of
`alanine or, in the case of L-alanine being the parent amino acid,
`elevated glucose levels; it stimulates proinsulin gene expres-
`the amino acid found in the corresponding position of glucagon.
`(4, 6-8). Accordingly,
`sion and inhibits glucagon secretion
`GLP-1 has a potential impact on glucose metabolism at several
`EXPERIMENTAL. PROCEDURES
`levels and has recently shown promising glucose-lowering ef-
`Peptide Synthesis-The peptides
`in Table I were synthesized using
`fects in non-insulin-dependent diabetes mellitus patients when
`the ABIMED 422 multiple synthesizer. The nomenclature utilized
`is
`administered in pharmacological doses (9-11).
`based on the sequence of GLP-1 (Fig. 1). 9-Fluorenylmethoxycarbonyl
`The sequence of GLP-1 is completely conserved in all mam-
`strategy, modified according to Gausepohl et al. (26), was used starting
`from a Rink-resin (NovaBiochem). The side-chain protection was
`as
`malian species investigated so far (1, 4, 12-15). The active
`follows: Am, Gln, His (trityl), Arg (2,2,5,7,8-pentamethylchroman-6-
`products of the proglucagon peptide (GLP-1, glucagon-like pep-
`(tert-butyl), and Trp and Lys
`sulfonyl), Asp, Glu, Tyr, Ser, and Thr
`tide-2, and glucagon), together with gastric inhibitory peptide,
`(tert-butyloxycarbonyl) (NovaBiochem). Each reaction vessel was filled
`form one branch of the growth hormone-releasing factor (GRF)
`with 25 pnol of resin. The peptides were cleaved from the resin and side
`superfamily of peptides. The members of this superfamily are
`
`chain deprotected
`trifluoroacetic acid/triethylsilane/water
`in
`(92.5:5:2.5) for 120 min and precipitated in tert-butylmethyl ether,
`believed to be derived from a common ancestor (16). The other
`washed twice with diethyl ether, and lyophilized from 10% acetic acid.
`branch of the GRF superfamily comprises pituitary adenylyl
`The crude peptides were purified by reverse phase HPLC using a gra-
`cyclase-activating peptide, vasoactive
`intestinal peptide, pep-
`dient of acetonitrile in water (1540% acetonitrile in 0.01 M HCl; col-
`tide histidine isoleucine amide, secretin, and GRF. The high
`umn, Superpak Pep S C2/C18, 5 p n ,
` 250 x 9.3 mm (Pharmacia LKB
`degree of sequence homology among the GRF superfamily is
`Biotechnology Inc.)).
`The purified peptides were characterized by analytical HPLC and
`high performance capillary electrophoresis as previously described (27)
`and were all of a purity of >95%. Molecular masses were measured by
`plasma desorption mass spectrometry analysis performed in positive
`mode on a 2s2Ca time of flight mass spectrometer (Bio-Ion) and were in
`agreement with the calculated mass within +2 mass units.
`Iodination ofDucer-Iodination of GLP-1 was performed by the lac-
`toperoxidase method (28). Purification by HPLC as previously described
`(29) afforded [1261-Tyr1glGLP-1-(7-36)-amide with a specific activity of
`76 kBq/pmol.
`6275
`
`* The costs of publication of this article were defrayed in part by the
`payment of page charges. This article must therefore be hereby marked
`“advertisement” in accordance with 18 U.S.C. Section 1734 solely
`to
`indicate this fact.
`$ To whom correspondence should be addressed. ”el.: 45-4442-3206;
`Fax: 45-4444-0993.
`The abbreviations used are: GLP-1, glucagon-like peptide-1-(7-36)-
`amide; GRF, growth hormone-releasing
`factor; HPLC, high pressure
`liquid chromatography; CHL, Chinese hamster lung.
`
`MPI EXHIBIT 1005 PAGE 1
`
`MPI EXHIBIT 1005 PAGE 1
`
`

`

`6276
`
`Structure-Activity of GLP-1
`
`Peptide
`
`7
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`GLP-I
`Exendin-4
`GLP-2
`Glucagon
`GIP
`VIP
`Secretin
`PACAP-38
`PHI
`GRF
`
`N
`
`
`
`&de
`P S S G A P P P S m i d e
`I T D R
`
`K G K K N D W K H N I
`
` T Q
`
`aY K Q R V
`
`
`
`K
`
`Ksmide
`
`Q Q G E S N Q E R G A R A R L ~ ~ L
`
`"-L\\
`
`FIG. 1. Comparison of the GLP-1 sequence to the sequence of other peptides in the GRF superfamily and the sequence of
`Exendin-4. Dark areas represents regions of homology. Position numbers refer to the nomenclature used for GLP-1 (position 7 corresponds to
`position 1 of the other peptides).
`
`Circular Dichroism Spectroscopy-Peptides were dissolved in 10 rn
`phosphate buffer, pH 6.5. Concentrations were determined by U V ab-
`sorbance using a molar absorption coefficient, ezs0, of 6970 M - ~ cm".
`Far-UV CD spectra were recorded with a Jobin Mark V dichrograph
`calibrated with (+)-10-camphorsulfonic acid. All spectra were recorded
`at room temperature using a 0.01-cm cell pathlength and a peptide
`concentration of about 0.5 mg/mL All spectra were smoothed by a Fou-
`rier transform algorithm before subtraction of the appropriate solvent
`blanks. The result, Ae, is based on the molar concentration of peptide
`bond.
`GLP-1 Receptor Binding Assay-Receptor binding was analyzed us-
`ing plasma membranes prepared from Chinese hamster lung (CHL)
`cells expressing the cloned rat pancreatic GLP-1 receptor (17). Cells
`were cultured in Dulbecco's modified Eagle's F-12 medium containing
`17.5 rn D-glucose, 10% fetal calf serum, 1 rn sodium pyruvate, 0.5
`g/liter lactalbumin, 100 IU/ml penicillin, 100 p g / d streptomycin, and
`
`80 pg/ml Geneticin" G-418 (Life Technologies, Inc.). Plasma membranes
`were prepared by resuspending the cells in cold buffer (10 rn Tris-HCI,
`pH 7.5, containing 30 rn NaCI, 1 rn dithiothreitol, 5 mg/liter leupep-
`tin, 5 mg/liter pepstatin, 100 mgfliter bacitracin (Sigma), and 15 mg/
`liter recombinant aprotinin (Novo Nordisk)), homogenization by two
`10-s bursts using a Polytron PT 10-35 homogenizer (Kinematica), and
`centrifugation on a layer of 41% (w/v) sucrose at 95,000 x g for 75 min.
`The white band located between the two layers was diluted in buffer
`and centrifuged at 40,000 x g for 45 min. The precipitate containing the
`plasma membranes was suspended in buffer and stored at -80 "C until
`required.
`The receptor binding assay was performed in 96-well 0.65-pm filter
`microtiter plates (Millipore). The buffer used was 50 rn HEPES (pH
`7.4) containing 2.5% human serum albumin grade V (Sigma). The pep-
`tide was dissolved in 100 p1 of buffer. Tracer (1.13 kBq, 25 pl of buffer)
`and 5 pg of freshly thawed plasma membrane suspended in 25 pl of
`buffer were added, and the plates were incubated for 30 min at 30 "C.
`Bound and unbound peptide were separated using a vacuum manifold
`(Millipore). Filters were washed with 125 pl of buffer and left to dry for
`2 h. The filters were then separated using the Millipore Punch System,
`and the amount of bound tracer was determined.
`Adenylyl Cyclase Assay-Adenylyl cyclase activity was assayed using
`plasma membranes prepared from the rat insulinoma cell line RIN
`2A18. Cells were cultured in media as above with the addition of 5
`mg/liter porcine insulin (Novo Nordisk), 1 g/liter dextran T-70 (Phar-
`macia), 10 mg/liter
`recombinant aprotinin (Novo Nordisk), and 0.5
`gfliter e-aminocaproic acid (Sigma). Plasma membranes were prepared
`as above.
`The incubation was camed out in microtiter plates in a total volume
`of 100 pl. Peptide and 2 pg of freshly thawed plasma membrane protein
`were diluted in 50 rn Tris buffer, pH 7.4, containing 0.1% human
`serum albumin grade V, 1 rn EGTA, 2 rn MgC12, 1 rn ATP, 0.5 rn
`3-isobutyl-l-methylxanthine, 15 rn creatine phosphate, 0.5 m g / d cre-
`atine kinase (Sigma). The mixture was incubated for 10 min at room
`temperature. The reaction was stopped by heating the plates to 80 "C
`for 3 min. The CAMP formed was measured using SPA-RIA (RPA.538,
`Amersham Corp.).
`
`RESULTS AND DISCUSSION
`GLP-1 Analogs-L-Alanine
`is the smallest optically active
`amino acid and is not able to fill the same space as any other
`amino acid except glycine. Furthermore, L-alanine has a high
`a-helix propensity and an exchange with this amino acid within
`
`100
`
`g 40 8 20
`
`m o
`.5
`
`
`I2
`
`I 1
`
`10
`
`9
`
`". 8
`
`I
`
`6
`
`Concentration of peptide (-log M)
`FIG. 2. Displacement of binding of [lzaI-Tyrls]GLF"l to plasma
`membranes from CHL cells expressing the cloned rat pancre-
`atic GLF"1 receptor with selected GLP-1 analogs. Each point rep-
`resents the mean of three determinations using plasma membranes
`from a single preparation, or for native GLP-1 the mean of 92 determi-
`nations using plasma membranes from 10 preparations. Assay condi-
`tions were as indicated under "Experimental Procedures." W, GLP-1; 0,
`[Alal21GLP-1; 0, [Alal61GLP-1; 0, [AlaZ8]GLP-1.
`
`an a-helix is generally unlikely to disrupt the helix. Accord-
`ingly, by substituting each amino acid in GLP-1 successively
`with L-alanine, positions with side chains important for recep-
`tor binding andor receptor activation may be detected. In
`GLP-1, t-alanine is found in positions 8,24, 25, and 30. To test
`the importance of these positions substitutions were made re-
`placing alanine with the amino acid found in the corresponding
`position in glucagon. As indicated in Fig. 1, glucagon is the
`to GLP-1
`peptide sharing the highest degree of homology
`among the related peptides in the superfamily. Even so, gluca-
`gon shows almost no affinity for the GLP-1 receptor (17).
`Receptor Affinity Studies-Competitive receptor binding was
`measured for all GLP-1 analogs using plasma membranes de-
`rived from a CHL cell line expressing the cloned GLP-1 recep-
`tor from rat pancreatic islets (17). IC50 for GLP-1 was meas-
`ured as 0.27 m in this system (Fig. 2). The binding afflnity of
`the GLP-1 analogs measured is shown in Table I.
`As indicated, substitution with L-alanine causes a great loss
`of receptor affinity when made in positions 7,10,12,13,15,28,
`and 29 (ICso > 10 m). The identification of positions 7,10, and
`15 as important for receptor binding is in agreement with pre-
`vious observations (23, 24) while positions 12, 13, 28, and 29
`have not previously been identified as important. Position 17
`was also indicated by Kawai et al. (23) as important for receptor
`binding. However, their conclusion was made based on an ana-
`log replacing Ser17 in GLP-1 with an arginine residue, thereby
`introducing a charged group in this position. Our data reveal
`almost no effect of substituting Ser17 with L-alanine (IC50 =
`0.46 m), and this position seems, accordingly, not to be in-
`volved in receptor binding. The greatest impact on receptor
`binding was observed by introducing L-alaNne in position 28
`(IC5o = 531 I"),
`thereby removing the hydrophobic PheZ8 resi-
`due, Interestingly, no effect was observed by introducing resi-
`dues from glucagon in positions 8,24, and 30 having alanine as
`
`MPI EXHIBIT 1005 PAGE 2
`
`MPI EXHIBIT 1005 PAGE 2
`
`

`

`TABLE I
`In vitro activity of various GLP-1 analogs
`Activities were measured as indicated under "Experimental Proce-
`dures." Binding affinity is expressed as mean + S.E. (n = 3, or in the case
`of native GLP-1, n = 92) while adenylyl cyclase activity is mean + S.E.
`(n = 2, or in the case of native GLP-1, n = 19).
`activity, Ec,
`
`Analog
`
`Binding affinity, ICm
`
`Structure-Activity of GLP-1
`
`6277
`
`Adenylyl c clase
`
`GLP- 1
`[Ala71GLP-1
`[SelBlGLP-1
`[AlaslGLP-l
`[Ala'OIGLP-1
`[AlallIGLP-l
`[Alalz]GLP-l
`[Alal31GLP-1
`[Alal41GLP-1
`[Alal51GLP-1
`[Ala16]GLP-1
`[Alal71GLP-1
`[Alal81GLP-1
`
`[AlalS1GLP-1 3.5
`
`[Alaz01GLP-1
`[Alaz11GLP-1
`[Alaz21GLP-l
`[Alaz31GLP-1
`[Argz4IGLP-1
`[AlaS]GLP-1
`[AlaZ7]GLP-1
`[Alaz81GLP-1
`
`
`[AlazslGLP-l 25
`[Gln3O1GLP-1
`[Ala3l1GLP-1
`[Ala32]GLP-1
`[Ala331GLP-1
`[Ala341GLP-1
`[Ala351GLP-1
`[Ala361GLP-1
`
`nM
`0.27 + 0.09
`30 + 5
`
`2.4 + 0.4 2.0
`8.1 f 1.0
`59 2 4
`3.5 2 0.3
`36 + 2
`36 + 6
`0.76 + 0.13
`11 2 1
`1.7 2 0.5
`0.46 + 0.10
`0.68 ? 0.09
`2 0.8
`1.7 + 0.1
`4.1 + 0.2
`0.57 + 0.08
`1.1 + 0.2
`0.89 + 0.20
` 17
`1.4 + 0.3
`0.24 2 0.04
`351 2 49
`2 3
`1.4 + 0.1
`1.6 + 0.2
` 15
`4.7 + 1.0
`1.4 + 0.2
`1.7 2 0.3
`1.3 2 0.1
`4.6 + 0.6
`
`nM
`2.6 + 0.4
`>lo4
`+ 0.3
`2 + 1
`> 104
`5 ? 2
`33 + 38
`65 2 49
`5 2 4
`>lo4
`7 + 5
`3 2 2
`2 2 1
`55 + 33
`7 + 1
`65 + 49
`4 2 1
`5 + 3
`2 10
`13 2 10
`1 2 1
`2,600 + 780
`70 2 14
`0.5 + 0.2
`+ 13
`4 2 3
`2 + 0
`2 2 0
`1 + 1
`7 t 5
`
`the parent amino acid in GLP-1. Even substitution with the
`charged L-arginine in position 24 had almost no impact on the
`receptor affinity (IC50 = 0.89 m).
`The accumulation of important residues in the N-terminal
`region of GLP-1 (positions 7, 10, 12, 13, and 15) suggests this
`part of the molecule to be most important for receptor binding.
`Surprisingly, positions 7,10, 12, and 13 are the most conserved
`positions among the peptides in the GRF superfamily (Fig. 1).
`Position 15 appears less conserved, but the differences among
`the members of the family represent substitutions that are
`mostly conservative, e.g. aspartic acid to glutamic acid. The
`N-terminal part of the peptide has also been found to be highly
`important for receptor binding in other members of the super-
`family where detailed structure-activity studies have been per-
`formed (30-32). Accordingly, although the N-terminal region of
`the peptides is highly important for receptor binding, it is un-
`likely that it is responsible for the selective recognition of the
`respective specific receptors. More likely, the N-terminal region
`is carrying a common message important for activation of the
`receptor. This hypothesis is supported by the observation that
`Exendin-449-39) is able to completely antagonize GLP-1 (19).
`Compared with the N-terminal domains, the C-terminal part of
`the peptides is much more heterogenous and thus more likely
`to be involved in specific receptor recognition. Similar ideas
`have been proposed previously based on the glucagon-glucagon
`receptor system by Hruby et al. (33). Based on our data, posi-
`tions 28 and 29 in GLP-1 are most important for receptor bind-
`ing in the C-terminal domain and could, accordingly, be deter-
`mining the specific interaction between GLP-1 and its receptor.
`Interestingly, the only peptide in Fig. 1 that is homologous to
`GLP-1 in all the important positions identified is Exendin-4,
`which is a very potent agonist of GLP-1 action (19).
`
`"
`
` 5
`
`I 2 1 1 10
`8
`9
`6
`1
`Concentration of pcptide (-log M)
`FIG. 3. Adenylyl cyclase activity of selected GLF"1 analogs
`RIN 2AlS
`measured using plasma membranes derived from
`cells. Each point represents the mean of two determinations using
`plasma membranes from a single preparation, or for native GLP-1 the
`mean of 19 determinations using plasma membranes from two prepa-
`rations. Assay conditions were as indicated under 'Experimental Pro-
`cedures." m, GLP-1; 0, [Alal51GLP-1; 0, [AlaZSIGLP-l; 0, [AlaS41GLP-1.
`
`S I
`
`
`
`-6 '
`
`170
`
`I
`
`I
`260
`
`200
`
`230
`
`Wavelength (nm)
`FIG. 4. Far-W CD spectra of GLP-1 (-)
`and analogs that
`cause significant spectral changes, Le. [Ala"]GLF"l
`[AlaSglGLP-l (- - -). Spectra were recorded in 10 n m phosphate buffer,
`and
`pH 6.5, using a 0.01-cm cell pathlength.
`
`( " 0 )
`
`Receptor Activation-Plasma membranes derived from the
`rat insulinoma cell line RIN 2A18 were used to measure recep-
`tor activation as they showed a much higher CAMP response
`than the plasma membranes
`from the CHL cell line. Using
`these membranes, the ECS0 for GLP-1 with respect to activa-
`tion of adenylyl cyclase is 2.6 m (Fig. 3). The binding affinity
`for GLP-1 of the membranes (IC50 = 0.44 m 2 0.06, n = 5 ) was
`found to be comparable with the affinity obtained with mem-
`branes from the CHL cell line (IC50 = 0.27 nM, Table I).
`Overall, analogs with a low receptor affinity were also found
`to have a higher EC50 with respect to activation of adenylyl
`cyclase (Table I). In agreement with the above hypothesis, sub-
`stitutions in the N-terminal positions 7 and 10 were found to
`have the most dramatic impact on receptor activation as none
`of these analogs showed any measurable effect on CAMP for-
`mation.
`The analog with L-alanine substitution in position 15, exhib-
`iting a relative high binding affinity (IC50 = 11 m) but no
`> 10 p d , was inves-
`ability to activate adenylyl cyclase
`tigated for its ability to antagonize GLP-1 action. Interestingly,
`the best glucagon antagonists described so far have an amino
`acid replacement in the same position (34). However, using 10
`m GLP-1, no antagonist effects could, unexpectedly, be ob-
`served at concentrations of up to 100 p [Alal51GLP-1.
`Circular Dichroism Measurements-Based on their low bind-
`ing affinity (IC50 > 10 m), GLP-1 analogs with L-alanine sub-
`stitution in positions 7, 10, 12, 13, 15,28, and 29 were selected
`for far-UV CD spectroscopy and compared with native GLP-1 to
`investigate possible conformational changes induced
`by the
`substitution.
`The far-UV CD spectrum of native GLP-1 was found to be
`constant in the pH range of 5.5-7.5, indicating a helical content
`of about 35%. At pH 6.5, CD spectra of the analogs were found
`to be very similar to that of native GLP-1, except for the ones
`with L-alanine substitution in positions 28 and 29 (Fig. 4).
`These analogs gave a significantly smaller CD indicating that
`
`MPI EXHIBIT 1005 PAGE 3
`
`MPI EXHIBIT 1005 PAGE 3
`
`

`

`6278
`
`Acknowledgments-The dedicated assistance of Pia Justesen, Vibeke
`Lykke, and Mette H. Frost-Jensen, the plasma desorption mass spec-
`trometry measurements by Per Franklin Nielsen, and the CD measure-
`ments by Anne-Marie Kolstrup are highly appreciated.
`
`the substitution had disrupted
`structure of the molecule.
`results of our structure-activity studies
`Conclusions-The
`support the conclusion that the residues His7, GlylO, PheL2,
`Thr13, and Asp15 contain side chains important for receptor
`interaction as substitution with L-alanine in these positions
`provides analogs with reduced receptor affhity and reduced
`capacity of activating adenylyl cyclase. Substitution of PheZ8
`and IleZ9 with L-alanine also provides analogs with reduced
`receptor affinity and activation. However, CD spectroscopy re-
`veals that the latter substitutions introduce a change in the
`secondary structure of the peptide while none of the former
`substitutions cause significant change. Rather than being in-
`volved in the receptor interaction, PheZ8 and IleZ9 may, conse-
`quently, be more important for the secondary structure of the
`peptide and consequently for the conformation being recog-
`nized by the receptor.
`The importance of the residues identified is further high-
`lighted as the only known agonist of GLP-1, Exendin-4, is ho-
`mologous to GLP-1 in all these positions.
`
`Structure-Activity of GLP-1
`Drucker, D. J., Philippe, J., Mosjov, S., Chick, W. L., and Habener, J. F. (1987)
`part of the alledged helical
`8.
`P m . Natl. Acad. Sci. U. S. A. 84,3434-3438
`Nathan, D. M., Schreiber, E., Fogel, H., Mosjov, S., and Habener, J. F. (1992)
`9.
`Diabetes Care 15,270-276
`Gutniak, M., Orskov, C., Holst, J. J., Ahdn, N., and Efendic, S. (1992) N. Engl.
`10.
`J. Med. 326, 1316-1322
`Nauck, M. A., Kleine, N., Orskov, C., Holst, J. J., and Creutzfeldt, W. (1993)
`11.
`Diabetologia 36,741-744
`Heinrich, G., Gros, P., Lund, P. K., and Habener, J. F. (1984) J. BWC. Chem. 259,
`12.
`716-718
`Lopez, L. C., Fraizer, M. L., Su, C . J., Kumar, A,, and Saunders, G. F. (1983)
`13.
`Proc. Natl. A c a d . Sci. U. S. A. 80,54854489
`Seino, S., Welsh, M., Bell, G. I., Chan, S. J., and Steiner, D. F. (1986) FEBS
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