Studies on the synthesis of insulin from natural and synthetic A and B chains. I. Splitting of insulin and isolation of the S-sulfonated derivatives of the A and B chains

Making, Cloning, and the Expression of Human Insulin Genes in Bacteria: The Path to Humulin

In the mid- to late 1970s, recombinant deoxyribonucleic acid methods for cloning and expressing genes in E. coli were under intense development. The important question had become: Can humans design and chemically synthesize novel genes that function in bacteria? This question was answered in 1978 and in 1979 with the successful expression in E. coli of 2 mammalian hormones, first somatostatin and then human insulin. The successful production of human insulin in bacteria provided, for the first time, a practical, scalable source of human insulin and resulted in the approval, in 1982, of human insulin for the treatment of diabetics. In this short review, I give my personal view of how the making, cloning, and expressing of human insulin genes was accomplished by a team of scientists led by Keiichi Itakura, Herbert W. Boyer, and myself.

New analogs of the CART peptide with anorexigenic potency: the importance of individual disulfide bridges

The CART (cocaine- and amphetamine-regulated transcript) peptide is an anorexigenic neuropeptide that acts in the hypothalamus. The receptor and the mechanism of action of this peptide are still unknown. In our previous study, we showed that the CART peptide binds specifically to PC12 rat pheochromocytoma cells in both the native and differentiated into neuronal phenotype. Two biologically active forms, CART(55-102) and CART(61-102), with equal biological activity, contain three disulfide bridges. To clarify the importance of each of these disulfide bridges in maintaining the biological activity of CART(61-102), an Ala scan at particular S-S bridges forming cysteines was performed, and analogs with only one or two disulfide bridges were synthesized. In this study, a stabilized CART(61-102) analog with norleucine instead of methionine at position 67 was also prepared and was found to bind to PC12 cells with an anorexigenic potency similar to that of CART(61-102). The binding study revealed that out of all analogs tested, [Ala(68,86)]CART(61-102), which contains two disulfide bridges (positions 74-94 and 88-101), preserved a high affinity to both native PC12 cells and those that had been differentiated into neurons. In food intake and behavioral tests with mice after intracerebroventricular administration, this analog showed strong and long-lasting anorexigenic potency. Therefore, the disulfide bridge between cysteines 68 and 86 in CART(61-102) can be omitted without a loss of biological activity, but the preservation of two other disulfide bridges and the full-length peptide are essential for biological activity.

Chemical synthesis of [des(tetrapeptide B27--30), Tyr(NH2)26-B] and [des(pentapeptide B26--30), Phe(NH2)25-B] bovine insulins

Two analogs of bovine insulin, [des(tetrapeptide B27--30), Tyr(NH2)26-B] and [des(pentapeptide B26--30), Phe(NH2)25-B] insulin, which differ from the parent molecule in that the C-terminal tetrapeptide and pentapeptide sequences, respectively, from the B chain have been eliminated and the newly exposed residues are amidated, have been synthesized. The [des(tetrapeptide B27--30), Tyr(NH2)26-B] insulin shows potencies of 16.8 IU/mg by the mouse convulsion assay method and 10.8 IU/mg by the radioimmunoassay method. The [des(pentapeptide B26--30), Phe(NH2)25-B] insulin possesses a potency of 10.5 IU/mg when assayed by the mouse convulsion method and 14 IU/mg by the radioimmunoassay technique. The potencies of these analogs are higher than the potencies of the respective non-amidated derivatives (Katsoyannis et al., 1973, 1974). It is speculated that the gradual decline of biological activity observed as amino acid residues are eliminated from the C-terminal region of the B chain of insulin is due to the proximity of a hydrophilic carboxyl group to the hydrophobic core of the protein molecule.

The Greek contribution to diabetes research

Interest in diabetes mellitus research has escalated in Greece during the last decade. This may be attributed to the realization that diabetes is becoming a major problem for the Greek population, the effect of the St Vincent Declaration in passing specific government legislation, and the founding of the National Hellenic Center for the Prevention and Treatment of Diabetes and its Complications. Research areas include epidemiology, etiopathogenesis, glucose metabolism, complications, prevention and treatment of the disease.

Mini-proinsulin and mini-IGF-I: homologous protein sequences encoding non-homologous structures

Protein minimization highlights essential determinants of structure and function. Minimal models of proinsulin and insulin-like growth factor I contain homologous A and B domains as single-chain analogues. Such models (designated mini-proinsulin and mini-IGF-I) have attracted wide interest due to their native foldability but complete absence of biological activity. The crystal structure of mini-proinsulin, determined as a T3R3 hexamer, is similar to that of the native insulin hexamer. Here, we describe the solution structure of a monomeric mini-proinsulin under physiologic conditions and compare this structure to that of the corresponding two-chain analogue. The two proteins each contain substitutions in the B-chain (HisB10-->Asp and ProB28-->Asp) designed to destabilize self-association by electrostatic repulsion; the proteins differ by the presence or absence of a peptide bond between LysB29 and GlyA1. The structures are essentially identical, resembling in each case the T-state crystallographic protomer. Differences are observed near the site of cross-linking: the adjoining A1-A8 alpha-helix (variable among crystal structures) is less well-ordered in mini-proinsulin than in the two-chain variant. The single-chain analogue is not completely inactive: its affinity for the insulin receptor is 1500-fold lower than that of the two-chain analogue. Moreover, at saturating concentrations mini-proinsulin retains the ability to stimulate lipogenesis in adipocytes (native biological potency). These results suggest that a change in the conformation of insulin, as tethered by the B29-A1 peptide bond, optimizes affinity but is not integral to the mechanism of transmembrane signaling. Surprisingly, the tertiary structure of mini-proinsulin differs from that of mini-IGF-I (main-chain rms deviation 4.5 A) despite strict conservation of non-polar residues in their respective hydrophobic cores (side-chain rms deviation 4.9 A). Three-dimensional profile scores suggest that the two structures each provide acceptable templates for threading of insulin-like sequences. Mini-proinsulin and mini-IGF-I thus provide examples of homologous protein sequences encoding non-homologous structures.

Anomalous mobility of sulfitolysed proteins in SDS-PAGE. Analysis and applications

Some cysteine-containing proteins upon sulfitolysis have been found to show anomalously retarded SDS-PAGE mobilities in non-reducing gels. These proteins include bovine serum albumin, ovalbumin, aldolase, ribonuclease and a recombinant fusion protein (XA) consisting of a portion of gamma-interferon linked to the A chain of human insulin. This mobility shift has been employed to determine the stability of the sulfonated products and to study the kinetics of the sulfitolysis reaction. Partially sulfonated products of intermediate shifts were observed at 0.01% beta-ME, while 0.05% beta-ME gave a shift characteristic of the completely reduced protein. The undiluted sulfitolysis reagent reacted with XA to give within 1 min a gel shift characteristic of the fully sulfitolysed protein. Its transition stages could be visualized at 15, 30 and 60 min when the reagent was diluted four-fold. In the presence of 8 M urea, the sulfitolysis of BSA was nearly complete at 30 min when the sulfitolysis reagent was used at a dilution of 1:5. However, under the same conditions BSA was predominantly unsulfitolysed in the absence of urea. In order to elucidate the mechanism of sulfonation shift, several derivatives of XA, e.g. performic acid oxidized, alkylated with (a) iodoacetamide and (b) iodoacetate, have been prepared. While the mobility of XASSO3- was sensitive to the presence of beta-ME, all other derivatives moved in a beta-ME-insensitive fashion. Furthermore, while the nonreducing mobilities of the acidic derivatives (-SSO3-, -SO3- and -SCH2CO2-) were anomalously retarded and identical, the mobility of the iodoacetamide derivative was intermediate between the retarded acidic derivatives above and XA below. These studies have suggested a role of the extended conformation of the A chain of insulin in causing a mobility shift of the acidic derivatives in this series. Similar results were observed in an analogous series of derivatives prepared from BSA. Non-denaturing gel filtration analyses of native vs. sulfitolysed samples of serum albumin, ovalbumin and ribonuclease have indicated that the sulfitolysed proteins elute earlier than their native counterparts and appear to be significantly larger than their true molecular weights. Circular dichroism analysis has indicated significant loss in helicity of sulfitolysed BSA. This suggests that the retarded mobility of sulfitolysed proteins seen on SDS-PAGE is likely to be due to an expansion in the hydrodynamic volumes of these proteins, a phenomenon triggered by cleavage of disulfide bonds and further accentuated by the introduction of strongly negatively charged sulfonates.

5-Hydroxytryptophan: an absorption and fluorescence probe which is a conservative replacement for [A14 tyrosine] in insulin

Use of insulin's intrinsic tyrosine absorption and fluorescence to monitor its interaction with the insulin receptor is limited because the spectral properties of the receptor tryptophan residues mask the spectral properties of the hormone tyrosine residues. We describe the synthesis of an insulin analog where A14 tyrosine is replaced by a tryptophan analog, 5-hydroxytryptophan. This insulin is spectrally enhanced since 5-hydroxytryptophan has an absorption band above 300 nm which is at lower energies than the absorption of tryptophan. Steady-state and time-resolved fluorescence parameters indicate that 5-hydroxytryptophan reports the same information about the environment of the A14 side chain as does the corresponding tryptophan-containing insulin. The synthetic hormone is a full agonist compared to porcine insulin, but has slightly reduced specific activity. Consequently, this spectrally enhanced insulin analog will be useful for hormone-receptor interaction studies since it can be observed by both absorption and fluorescence even in the presence of the tryptophan-containing receptor.

Contribution of the B16 and B26 tyrosine residues to the biological activity of insulin

We report the synthesis and biological evaluation of five insulin analogues in which one or both of the B-chain tyrosine residues have been substituted. [B16 Phe]insulin and [B16 Trp]insulin display a very modest reduction in potency (c. 65%) relative to porcine insulin; [B26 Phe]insulin is less active (30-50%), and the doubly substituted [B16 Phe, B26 Phe]insulin displays still lower potency (c. 35%). The further substitution of Asp for B10 His in [B16 Phe, B26 Phe]insulin raises its activity to approximately twofold greater than natural insulin, an increase of approximately fivefold over the parent compound. We conclude that the bulk and/or aromaticity of the amino acid residue at position B16, but not its hydrogen-bonding capacity, contributes to the biological activity of the hormone. We further conclude that hydrogen-bonding capacity or special side-chain packing characteristics are required at the B26 position for insulin to display high biological activity.

The effect of placement of tryptophan residues in selected A-chain positions on the biological profile of insulin

In continuation of our efforts to study the solution structure and conformational dynamics of insulin by time-resolved fluorescence spectroscopy, we have synthesized and examined the biological activity of five insulin analogues in which selected naturally occurring residues in the A-chain have been replaced with the strongly fluorescent tryptophan residue. The potency of these analogues was evaluated in lipogenesis assays in isolated rat adipocytes, in receptor binding assays using rat liver plasma membranes, and in two cases, in receptor binding assays using adipocytes. [A3 Trp]insulin displays a potency of 3% in receptor binding assays in both liver membranes and in adipocytes, but only 0.06% in lipogenesis assays as compared to porcine insulin. [A10 Trp]insulin displays a potency of ca. 40% and ca. 25% in rat liver receptor binding and lipogenesis assays, respectively. [A13 Trp]insulin displays a potency of ca. 39% in rat liver receptor binding assays, but only ca. 9% in receptor binding in adipocytes; in lipogenesis assays, [A13 Trp]insulin displays a potency of ca. 12%, comparable to its potency in adipocyte receptor binding assays. [A15 Trp]insulin exhibits a potency of 18% and 9% in rat liver receptor binding and lipogenesis assays, respectively. The doubly substituted analogue, [A14 Trp, A19 Trp] insulin, displays a potency of ca. 0.7% in both rat liver receptor binding assays and lipogenesis assays.(ABSTRACT TRUNCATED AT 250 WORDS)

The A14 position of insulin tolerates considerable structural alterations with modest effects on the biological behavior of the hormone

As part of our aim to investigate the contribution of the tyrosine residue found in the 14 position of the A-chain to the biological activity of insulin, we have synthesized six insulin analogues in which the A14 Tyr has been substituted by a variety of amino acid residues. We have selected three hydrophilic and charged residues--glutamic acid, histidine, and lysine--as well as three hydrophobic residues--cycloleucine, cyclohexylalanine, and naphthyl-(1)-alanine--to replace the A14 Tyr. All six analogues exhibit full agonist activity, reaching the same maximum stimulation of lipogenesis as is achieved with porcine insulin. The potency for five of the six analogues, [A14 Glu]-, [A14 His]-, [A14 Lys]-, [A14 cycloleucine]-, and [A14 naphthyl-(1)-alanine]-insulins in receptor binding assays ranges from 40-71% and in stimulation of lipogenesis ranges from 35-120% relative to porcine insulin. In contrast, the potency of the sixth analogue, [A14 cyclohexylalanine]insulin, in both types of assays is less than 1% of the natural hormone. The retention time on reversed-phase high-performance liquid chromatography for the first five analogues is similar to that of bovine insulin, whereas for the sixth analogue, [A14 cyclohexylalanine]insulin, it is approximately 11 min longer than that of the natural hormone. This suggests a profound change in conformation of the latter analogue. Apparently, the A14 position of insulin can tolerate a wide latitude of structural alterations without substantial decrease in potency. This suggests that the A14 position does not participate directly in insulin receptor interaction. Only when a substitution which has the potential to disrupt the conformation of the molecule is made at this position, is the affinity for the receptor, and hence the biological potency, greatly reduced.

Insulin analogues with modifications in the beta-turn of the B-chain

The beta-turn formed by the amino acid residues 20-23 of the B-chain of insulin has been implicated as an important structural feature of the molecule. In other biologically active peptides, stabilization of beta-turns has resulted in increases in activity. We have synthesized three insulin analogues containing modifications which would be expected to increase the stability of the beta-turn. In two analogues, we have substituted alpha-aminoisobutyric acid (Aib) for the Glu residue normally present in position B21 or for the Arg residue normally present in position B22; in a third compound, we have replaced the Glu residue with its D-isomer. Biological evaluation of these compounds showed that [B21 Aib]insulin displays a potency ca. one-fourth that of natural insulin, while [B22 Aib]insulin is less than 10% as potent. In contrast, [B21 D-Glu]insulin is equipotent with natural insulin. We conclude that the beta-turn region of the insulin molecule normally possesses considerable flexibility, which may be necessary for it to assume a conformation commensurate with high biological activity. If this is the case, [B21 D-Glu]insulin may exhibit a stabilized geometry similar to that of natural insulin when bound to the insulin receptor.

Superactive insulins

The substitution of aspartic acid for the naturally-occurring histidine residue in position B10 in human insulin results in an insulin analogue which displays an in vitro potency 4- to 5-fold greater than the parent compound. This substitution has been introduced into six insulin analogues which, before modification, display potencies ranging from less than 0.01-fold to 3-fold relative to natural insulin. In each case, the resulting aspartic acid-substituted analogue is substantially more potent than the parent compound. Thus, it is now possible to prepare "tailor-made" insulins with enhanced potency.

Inhibition of thrombin by synthetic hirudin peptides

To investigate the role of different regions of hirudin in the interaction with the proteinase thrombin, segments of hirudin containing 15-51 residues were synthesized. The C-terminal segment 40-65 inhibited the fibrinogen clotting activity of thrombin but not amidolysis of tosyl-Gly-Pro-Arg-p-nitroanilide. Central peptide 15-42 was insoluble at pH 7, but peptide 15-65 inhibited fibrinogen clotting and amidolysis to an equal extent. The N-terminal loop peptide 1-15 had no inhibitory activity and did not affect the potency of peptide 15-65. These data suggest that the central region inhibits catalysis.

An insulin-like hybrid consisting of a modified A-domain of human insulin-like growth factor I and the B-chain of insulin

We have synthesized an insulin-like compound, consisting of the B-chain of bovine insulin and an A-chain corresponding to the A-domain of human insulin-like growth factor-I (IGF-I), in which the isoleucine residue normally present in position 2 of the A-domain of IGF-I has been replaced with glycine. Biological evaluation of the compound indicated that its insulin-like activity (insulin receptor-binding and stimulation of lipogenesis) was 0.2%, and its growth-factor activity (stimulation of thymidine incorporation) was less than 1%, both relative to natural insulin. We conclude that interactions between IleA2 and TyrA19, which are crucial to high biological activity in insulin, are also present in IGF-I, and are equally critical for its biological activity.

An insulin-like compound consisting of the B-chain of bovine insulin and an A-chain corresponding to a modified A- and the D-domains of human insulin-like growth factor I

We report the synthesis and biological evaluation of a two-chain, disulfide-linked, insulin-like compound consisting of the B-chain of bovine insulin and an A-chain corresponding to the A- and D- domains of human insulin-like growth factor-I (IGF-I) in which the A-domain amino-acid residues -Phe49-Arg50-Ser51-found in IGF-I have been replaced by -Ala-Gly-Val-, the homologous region of sheep insulin. The compound is indistinguishable from a previously reported compound whose A-chain corresponds to the A- and D-domains of IGF-I without the substitution, in assays for insulin-like activity as well as in assays for growth-promoting activity. We conclude that these A-domain residues do not contribute significantly to the interaction of IGF-I with either insulin or IGF-I receptors.

A highly potent insulin: des-(B26-B30)-[AspB10,TyrB25-NH2]insulin(human)

An insulin analogue that embodies two distinct structural modifications, each of which independently increases insulin activity, has been synthesized and evaluated for biological activity. The analogue, des-(B26-B30)-[AspB10,TyrB25-NH2]insulin is the most potent insulin analogue yet described; it displays an 11- to 13-fold higher activity than natural insulin. The findings are discussed with regard to the receptor-binding domains of insulin.

Synthesis of an insulin analogue embodying a strongly fluorescent moiety, [19-tryptophan-A]insulin

As part of our aim to study the conformation of insulin in solution by time-resolved fluorescence spectroscopy, we have synthesized the analogue [19-Tryptophan-A]insulin. In this compound, the tyrosine residue at position 19 of the A-chain of insulin, one of the most strongly conserved residues in insulins from various species, is substituted with the strongly fluorescent tryptophan residue. [19-Tryptophan-A]insulin displays 4.1 +/- 1.9% of the potency of natural insulin in binding to the insulin receptor from rat liver plasma membranes, 5.0 +/- 2.3% in stimulating lipogenesis in rat adipocytes, and 75.7 +/- 4% of the potency of insulin in radioimmunoassay. In connection with our previous work, these data indicate that an aromatic side chain at position A19 of insulin seems necessary but not sufficient for high biological activity. We further conclude that in regard to the immunogenic determinants of insulin, tryptophan in position A19 is an essentially neutral substitution for tyrosine in that position, in sharp contrast to the situation with regard to biological activity.

Hybrid molecules containing the A-domain of insulin-like growth factor-I and the B-chain of insulin have increased mitogenic activity relative to insulin

Two synthetic insulin-like compounds consisting of the B-chain of insulin linked via disulfide bonds to A chains corresponding to the A-domain or the A- and D-domains of insulin-like growth factor I (IGF-I) have been evaluated for mitogenic activity and for binding to IGF receptors and IGF carrier proteins. Both compounds are 3- to 5-fold more potent mitogens than insulin, and have a comparably increased affinity for the type I IGF receptor that mediates these mitogenic effects in chick embryo fibroblasts. Neither compound interacts with IGF carrier proteins. These results indicate that the A-domain of IGF-I is importantly involved in its growth-promoting properties.

Effect of N-methylation of selected peptide bonds on the biological activity of insulin. [2-N-methylisoleucine-A]insulin and [3-N-methylvaline-A]insulin

Hydrogen bonding involving peptide bonds of the backbone of the insulin molecule may play an important role in insulin-receptor interaction. Our previous work suggested that the A2-A8 helical segment of the hormone molecule participates in this interaction. To investigate the possible involvement of peptide bonds of this segment in insulin-receptor interaction the [2-N-methylisoleucine-A]insulin and [3-N-methylvaline-A]insulin ([MeIle2-A]- and [MeVal3-A]insulins) were synthesized. The circular dichroic spectra of the analogues were obtained and their properties were examined in several biological assays. The circular dichroic spectra suggested that the analogues remained monomeric at concentrations at which insulin is predominantly dimeric, and that their A2-A8 helical segments are distorted. The in vitro biological activity and the receptor binding affinity of these analogues were compared with that of natural insulin. Both analogues are weak full agonists. [MeIle2-A]insulin displayed a potency of 5.4 +/- 0.3% in stimulating lipogenesis and 4.6 +/- 2.3% in receptor binding affinity in rat fat cells and rat liver plasma membranes respectively. [MeVal3-A]insulin displayed a potency of 2.1 +/- 0.2% in lipogenesis and 1.0 +/- 0.3% in receptor binding assays. In radioimmunoassays [MeIle2-A]- and [MeVal3-A]insulins exhibited potencies of 13% and 11% respectively relative to the natural hormone. The substantially decreased biological activity and receptor binding affinity of these analogues may be attributed partly to the change of conformation and partly to the loss of hydrogen bonding capacity of the A2-A8 segment brought about by N-methylation of the A1-A2 or A2-A3 peptide bonds.

A superactive insulin: [B10-aspartic acid]insulin(human)

The genetic basis for a case of familial hyperproinsulinemia has been elucidated recently. It involves a single point mutation in the proinsulin gene resulting in the substitution of aspartic acid for histidine-10 of the B chain of insulin. We have synthesized a human insulin analogue, [AspB10]insulin, corresponding to the mutant proinsulin and evaluated its biological activity. [AspB10]Insulin displayed a binding affinity to insulin receptors in rat liver plasma membranes that was 534 +/- 146% relative to the natural hormone. In lipogenesis assays, the synthetic analogue exhibited a potency that was 435 +/- 144% relative to insulin, which is statistically not different from its binding affinity. Reversed-phase HPLC indicated that the synthetic analogue is more apolar than natural insulin. We suggest that the observed properties reflect changes in the conformation of the analogue relative to natural insulin, which result in a stronger interaction with the insulin receptor. Thus, a single substitution of an amino acid residue of human insulin has resulted in a superactive hormone.

Interaction between the A2 and A19 amino acid residues is of critical importance for high biological activity in insulin: [19-leucine-A]insulin

The replacement of tyrosine at position A19 by leucine in the insulin molecule led to an analogue, [19-leucine-A]insulin [( Leu19-A]insulin), displaying insignificant receptor binding affinity and in vitro biological activity less than 0.1 and 0.05%, respectively, compared to the natural hormone. This analogue along with the previously reported [2-glycine-A]-, [2-alanine-A]-, and [2-norleucine-A]insulins is the least potent insulin analogue we have examined. Circular dichroic studies showed that all these analogues are monomeric at concentrations at which insulin is primarily dimeric. We conclude that an aromatic ring at position A19 and the presence of the side chain of isoleucine at position A2 are each of critical importance for high biological activity in insulin. It appears that the van der Waals interaction between the side chain of isoleucine A2 and tyrosine A19, present in crystalline insulin, is among the most important determinants for high biological activity in insulin.

Roles of the 29-138 disulfide bond of subtype A of human alpha interferon in its antiviral activity and conformational stability

Human alpha (leukocyte) interferons contain two disulfide bonds between Cys-1 and Cys-98 and between Cys-29 and Cys-138. Reduction of interferon under native conditions leads to irreversible loss of antiviral activity; reduction in denaturant, followed by oxidation in native conditions, leads to restoration of activity. This behavior, unusual for disulfide-containing proteins, was studied by using a thiosulfonate derivative of subtype A of human alpha interferon (IFN-alpha A). The disulfide-free thiosulfonate formed at 25 degrees C has essentially no antiviral activity, while maintaining a conformation related to that of native IFN-alpha A. This species can regain activity after regeneration of its 29-138 disulfide, by thiol-disulfide interchange in native buffer. Incubation of the disulfide-free thiosulfonate under nonreducing conditions at 37 degrees C generates a monomeric species that has lost its native conformation as well as its ability to regain antiviral activity after thiol-disulfide interchange. These results explain the difficulty in obtaining, under native conditions, a reduced species that regains activity upon oxidation; complete reduction of IFN-alpha A in 100 mM 2-mercaptoethanol requires 37 degrees C, a temperature that promotes conformational decay of the disulfide-free form.

Nature of the B10 amino acid residue. Requirements for high biological activity of insulin

Human [10-asparagine-B] insulin ([ Asn10 -B] insulin), an analogue which differs from the parent molecule in that the histidine residue at position 10 of the B chain (B10) is replaced by asparagine, has been synthesized and isolated in purified form. In vitro biological assays indicated a potency of ca. 35% compared to insulin. We have previously shown that the replacement of histidine at position B10 by lysine resulted in an analogue displaying ca. 15% of the biological activity of natural hormone, while the substitution of leucine in this position produced a molecule exhibiting ca. 45% potency in in vivo assays. The data indicate that molecular size of the amino acid residue at position B10 may be important in the maintenance of a structure commensurate with high biological activity. Polarity at this position appears to be rather unimportant while a strongly basic group appears to be deleterious.

Critical role of the A2 amino acid residue in the biological activity of insulin: [2-glycine-A]- and [2-alanine-A]insulins

We report the synthesis of [2-glycine-A]insulin ([ Gly2 -A]insulin) and [2-alanine-A]insulin ([ Ala2-A]insulin) in which the indicated amino acid has been substituted for isoleucine found in this position in the natural hormone. The circular dichroic (CD) spectra of the analogues were obtained, and their properties were examined in several biological assays. CD studies suggested that the analogues remain monomeric at concentrations at which insulin is partly or mostly dimeric. Both analogues are extremely weak full agonists. [ Gly2 -A]-insulin displays 0.05% of the potency of bovine insulin, whereas [Ala2-A]insulin assays at 0.4% of the activity of the natural hormone. We conclude that the presence of the side chain of isoleucine at position A2 is a critical requirement for high biological activity in insulin. The data, together with previous observations, are discussed in connection with an interaction between the side chain of isoleucine-A2 and the phenolic ring system of tyrosine-A19, which are in van der Waals contact in crystalline insulin. This interaction may be required to permit the molecule to assume a conformation consistent with dimerization and with binding to the insulin receptor.

An insulin analogue possessing higher in vitro biological activity than receptor binding affinity. [21-Proline-B]insulin

To study the effect of an increase in the potential for beta-turn formation of the B20-B23 segment of the B-chain moiety on the biological behavior of insulin, the [21-proline-B]insulin [( Pro21-B]insulin) was synthesized. The in vitro biological activity and the receptor binding affinity of this analogue were compared with that of insulin. In stimulating labeled glucose incorporation into lipids in rat fat cells, the analogue displayed 33.2% potency relative to insulin; receptor binding affinity for the analogue was 15.9% in rat liver membranes and 17.8% in isolated fat cells. [Pro21-B]insulin is thus the first example of a modified insulin for which the biological activity exceeds the receptor binding potency. The secondary structure of this analogue was investigated by circular dichroism studies. Although no significant differences in the conformation of monomeric insulin and analogue could be discerned, their difference in behavior with respect to dimerization and biological properties indicates that these forms are not equivalent. We suggest that the intrinsic activity of receptor-bound [Pro21-B]insulin is greater than that of insulin, although the receptor displays greater affinity for insulin than for the analogue. We consider a model for the interaction between insulin and its receptor that accommodates our findings.

Monoclonal antibodies can discriminate between some active and inactive forms of leukocyte interferon

Antiviral activity of recombinant human leukocyte A interferon was inactivated by heating at 65 degrees C or by reduction of disulfide bonds. The specific immunoreactivity, as measured by radioimmunoassays measuring binding to monoclonal antibodies, decreased concomitantly with the antiviral activity. Although the monoclonal antibodies did bind to inactivated interferon, their binding affinity to inactivated interferon was in general very much lower than their binding affinity to active interferon. Therefore, this immunoassay could replace the antiviral assay for detection of biologically active interferon. In addition, most of these antibodies should be especially useful for purification of the interferons since they discriminate between the native active and inactive denatured species. Screening for such antibodies is convenient and simple. The general use of antibodies that preferentially interact with native molecules provides a powerful new principle for choosing monoclonal antibodies with extraordinary potential in assay and purification.

[12-asparagine-B] human insulin. An analogue with modification in the hydrophobic core of insulin

The human [12-Asparagine-B] insulin [Asn12-B] insulin) which differs from the parent molecule in that the valine residue at position B12 is substituted by an asparagine residue, has been synthesized by the procedures developed in this laboratory. In stimulating glucose oxidation and lipogenesis the analogue exhibited potencies of 0.19% and 0.14%, respectively, as compared to insulin. In insulin receptor binding [Asn12-B] insulin was found to possess a potency of ca. 0.29% compared to the natural hormone. At high concentrations this analogue is shown to have the same maximal activity in the in vitro assays as the natural hormone. This indicates that despite the low affinity for of the analogue for the insulin receptor, the analogue-receptor complex is fully capable of initiating the series of chemical events that leads to the biological response. It is concluded that the B12 valine contributes greatly in the maintenance of a structure possessing the proper receptor-binding characteristics, but does not have any role in modulating the activity of the hormone-receptor complex. The potency of this analogue by radioimmunoassay is at least 100-fold higher than the in vitro biological assays, indicating that the immunological determinants of insulin can be essentially unrelated to the biological activity of the molecule.

Oxidation of the sulfhydryl forms of insulin A-chain and B-chain

A modified procedure for the preparation of the S-sulfonates of the A- and B-chains of insulin and their conversion to the sulfhydryl forms by tri-n-butylphosphine is described. Air oxidation of the sulfhydryl forms of the A-chain in dilute solution (0.2 mg/ml) either in the presence or absence of urea at pH 9.0 yields primarily monomeric, intrachain disulfides. Similar treatment of the reduced B-chain yield monomeric, intrachain disulfide in 7 M urea but a large number of oligomeric, interchain disulfides in the absence of urea. Electrolytic reduction of insulin in 7 M urea of pH 8.5, followed by oxidation of the sulfhydryls in dilute solution in 7 M urea at pH 9.0 yields primarily a mixture of the monomeric, intrachain disulfides of the A-chain and of the B-chain which can be separated by chromatography on Sp-Sephadex in acidic urea. The rate of the oxidation of the sulfhydryls of the two separate chains was much slower and less complete than that reported for the two chains crosslinked by the carbonylbismethionyl residue.

Synthesis of des(tetrapeptide B(1-4)) and des(pentapeptide B(1-5)) human insulins. Two biologically active analogues

Two analogues of human insulin, des(tetrapeptide B(1-4))-and des (pentapeptide B(1-5))-insulin, which differ from the parent molecule in that the N-terminal tetrapeptide and pentapeptide sequences, respectively, have been eliminated, have been synthesized. The des(tetrapeptide B(1-4))-insulin shows potencies of 13 IU/mg by the mouse convulsion assay method and 7.6 IU/mg by the radioimmunoassay method. The des(pentapeptide B(1-5))-insulin possesses a potency of 1.2 IU/mg when assayed by the glucose-oxidation method in isolated fat cells and 3.7 IU/mg by the radioimmunoassay technique. The natural hormone has a potency of 23--25 IU/mg by both assay methods.

Synthesis of two biologically active insulin analogues with modifications at the N-terminal and N- and C-terminal amino acid residues

The synthesis and isolation in purified form of two analogues of insulin is described. [21-Isoasparagine-A] ([Iasn21-A]) insulin differs from the parent molecule in that the amino acid residue, asparagine, found at the C terminus of the A chain (A21) has been replaced by isoasparagine. [Sar1, Iasn21-A] insulin differs from insulin in that both the A1 and A21 amino acid residues, glycine and asparagine, have been substituted by sarcosine and isoasparagine, respectively. The synthesis of these analogues followed the pattern employed in this laboratory for the synthesis of insulin and its analogues. The S-sulfonated derivatives of the A chain analogues were chemically synthesized, converted to their sulfhydryl forms, and then combined with the S-sulfonated B chain to produce the respective insulin analogues. Isolation of the insulin analogues from the combination mixtures was effected by chromatography on a carboxymethylcellulose column with an exponential sodium chloride gradient. By the mouse convulsion assay method [Iasn21-A]insulin possessed a potency of 21 IU/mg and [Sar1, Iasn21-A] insulin 15 IU/mg. The radioimmunoassay method gave values of 16 IU/mg for the former and 7IU/mg for the altter analogue. The natural hormone has a potency of 23-25 IU/mg by both assay methods. These data indicate that the alpha- and beta-carboxyl groups of the A21 amino acid residue are nearly equivalent in terms of their contribution to the expression of the biological activity of insulin. Furthermore, these data strengthen the speculation (Cosmatos, A., Johnson, S., Breier, B., and Katsoyannis, P. G. (1975), J. Chem. Soc. Perkin Trans. 1, 2157) that the change in the relative positive charge at the N-terminal amino acid residue of the A chain is responsible for the considerable decrease in the immunoreactivity observed in such modified insulins.

Synthesis of human [9-leucine-B] Insulin

The synthesis and isolation in purified form of [Leu9-B]insulin, a biologically active analogue of human insulin, is described. This analogue differs from the parent molecule in that the polar residue, serine, occupying position 9 in the B chain and located on the outside of the insulin molecule, has been replaced with the hydrophobic leucine residue. For the synthesis of this analogue the [Leu9]B chain of human insulin was chemically synthesized by the fragment condensation approach and isolated in the S-sulfonated form. Combination of this compound with the sulfhydryl form of human A chain afforded [Leu9-B]insulin. Separation of this analogue from the combination mixture and isolation as the hydrochloride in purified form were accomplished by chromatography on a carboxymethylcellulose column with an acetate buffer (pH 3.3) and an exponential sodium chloride gradient. [Leu9-B]Insulin possesses a potency of 13-14 IU/mg when assayed by the mouse convulsion method and 11-12 IU/mg by the radioimmunoassay method as compared to 23-25 IU/mg possessed by the natural hormone.

A comparison of the structure of hamster pancreatic insulin and insulin extracted from a transplantable hamster islet-cell carcinoma

Insulin has been isolated from pancreases of the Syrian hamster and from a transplantable islet-cell tumor of the hamster. Acid/ethanol extraction, ether precipitation, ion exchange and gel filtration chromatography gave preparations of suitable purity for structural studies. Using trypsin cleavage, automatic Edman degradation and manual Edman degradation, a complete sequence of the pancreatic insulin B chain was determined. By automatic Edman degradation, the amino-terminal 10 residues of the pancreatic A chain were assigned and the sequence of carboxy-terminal eleven residues could be deduced by homology to other mammalian and avian insulins. The sequence assigned to hamster insulin A chain is identical to that of the rat, mouse and spiny mouse. The sequence of hamster insulin B chain is identical to rabbit and spiny mouse B chain. In terms of protein evolution, hamster insulin thus appears to occupy an intermediate position between rabbit and rat insulins. Amino acid composition, tryptic peptide composition and partial sequence analysis of the hamster tumor insulin showed no differences from hamster pancreatic insulin.