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K S Iyer

Publications and source records attributed to K S Iyer.

At least 19 recordsLinked to original sources
PubMed2004

Identification of the structural and functional determinants of the extracellular domain of the human follicle stimulating hormone receptor.

The extracellular domain (ECD) of the human follicle-stimulating hormone receptor (hFSHR) is believed to be the major determinant of hormone selectivity. Different discrete, discontinuous regions on the ECD of the hFSHR have been suggested to be crucial for hormone binding. However, the role of the ECD in signal transduction is not well understood. This study provides some insight into these aspects of the structure-function relationship of the ECD of hFSHR. Ten peptides were selected from the ECD on the basis of their ability to be surface oriented, synthesized by the solid-phase method using fluorenylmethyloxycarbonyl chemistry, purified and characterized. They were further studied for their ability to modulate both human follicle-stimulating hormone (hFSH)-FSHR binding and cAMP generation. Competitive inhibition studies showed that, of all the peptides studied, peptides 285-300 and 297-310 hFSHR were able to inhibit hFSH binding to FSHR. Both peptides function as weak competitive inhibitors of hFSH-FSHR binding. Peptides 285-300 hFSHR, 216-235 hFSHR, 184-195 hFSHR, 79-89 hFSHR and 15-31 hFSHR were observed to inhibit FSH-induced cAMP production. In summary, this study suggests that discrete, functional domains of the ECD have a role in hormone binding and signal transduction. Region 285-300 has been identified as a novel region crucial for both FSH binding and cAMP generation.

Amino Acid Sequence↗
PubMed2003

Disulfide bonds Cys(9)-Cys(57), Cys(34)-Cys(88) and Cys(38)-Cys(90) of the beta-subunit of human chorionic gonadotropin are crucial for heterodimer formation with the alpha-subunit: experimental evidence for the conclusions from the crystal structure of hCG.

Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein hormone essential for the establishment and maintenance of pregnancy. The alpha- and beta-subunits of hCG are highly cross-linked internally by disulfide bonds that seem to stabilize the tertiary structures required for the noncovalent association of the subunits to generate hormonal activity. This paper describes the results of our studies on the role of the disulfide bonds of hCG-beta in heterodimer formation with the alpha-subunit. Six disulfide peptides incorporating each of the six disulfide bonds of hCG-beta were screened, along with their linear counterparts, for their ability to competitively inhibit the recombination of alpha- and beta-subunits. The disulfide peptides Cys (9-57), Cys (34-88) and Cys (38-90) were found to inhibit the alpha/beta recombination whereas the remaining three disulfide peptides viz. Cys (23-72), Cys (26-110) and Cys (93-100) did not exhibit any inhibition activity. Interestingly, none of the linear peptides could inhibit the alpha/beta recombination. Results clearly demonstrate that the disulfide bonds Cys(9)-Cys(57), Cys(34)-Cys(88) and Cys(38)-Cys(90) of the beta-subunit of hCG are crucial for heterodimer formation with the alpha-subunit thus providing experimental confirmation of the conclusions from the crystal structure of the hormone.

Amino Acid Sequence↗
PubMed2003

Effect of active immunization with the C-terminal 67-94 (R-28) region of human seminal plasma inhibin on the fecundity of adult male rabbits.

PROBLEM: To characterize the specificity of antibodies to the synthetic C-terminal 67-94 (R-28) peptide of human seminal plasma inhibin (hSPI), and to examine the effect of active immunization on the fecundity of adult male animals. METHOD OF STUDY: The specificity of R-28-DT antibodies was tested using enzyme-linked immunosorbent assay, immunohistochemical and immunofluorescence staining, and Western blotting. For fertility studies, adult male rats and rabbits were immunized and mated with females of the same strain. RESULTS: Rabbit antibodies to R-28-DT recognized native hSPI, as demonstrated by sperm agglutination in vivo and in vitro, on the sperm head by immunofluorescence staining, and in the columnar epithelial cells of the prostate by immunohistochemical staining. Immunization with the R-28-DT conjugate elicited a poor antibody response in male rats and their fecundity remained unaffected, while in male rabbits it elicited a good immune response with reduction in their fertility. CONCLUSION: R-28-DT antibodies recognized the native hSPI in the prostatic epithelium and agglutinated washed rat, rabbit, monkey, and human spermatozoa in vitro. Immunization of rabbits caused agglutination of spermatozoa resulting in a decrease in their fecundity. The conjugated R-28 peptide of hSPI offers promise as a male contraceptive.

Animals↗
PubMed2003

Attempt to map the receptor binding sites of human follicle-stimulating hormone using disulfide peptides of its beta-subunit indicates major involvement of the regions around disulfide bonds Cys28-Cys82 and Cys32-Cys84 in receptor binding of the hormone.

Follicle-stimulating hormone (FSH) is a heterodimeric glycoprotein hormone secreted by the anterior pituitary. It plays a very important role in folliculogenesis in females and is responsible for spermatogenesis in males. The alpha-subunit which is common within a species and the beta-subunit which is hormone-specific are held together by noncovalent association. This association is very essential for the biological activity of the hormone. Each of these subunits are highly cross-linked by disulfide bonds which appear to stabilize the tertiary structures required for the noncovalent association of the subunits to generate hormonal activity. This study was initiated to delineate the role of the disulfide bonds of hFSH beta in receptor binding of the hormone. Five intermolecular and one intramolecular disulfide peptides corresponding to the disulfide bonds found in hFSH beta were synthesized and screened along with their linear counterparts, for their ability to competitively inhibit the radiolabelled [125I]hFSH from binding to the FSH receptor containing membranes from the testis of immature rats. The disulfide peptides Cys28-Cys82 and Cys32-Cys84 were found to be the most potent in inhibiting radiolabelled hFSH from binding to its receptor. The results suggest the involvement of the regions around disulfide bonds Cys28-Cys82 and Cys32-Cys84 in receptor binding of the hormone. The studies also suggest the involvement of beta L2 and beta L3 loop regions in receptor binding of the hormone. This study is the first of its kind to use disulfide peptides rather than linear peptides to map the receptor binding regions of hFSH.

Amino Acid Sequence↗
PubMed2002

A detailed study of the L2beta long-loop region of human chorionic gonadotrophin suggests it to be spatially close to, but not part of, the receptor-binding site.

An in-depth study of the L2beta long-loop region of human chorionic gonadotrophin (hCG), earlier identified to be a conformational bioneutralization epitope and receptor-binding site of the hormone, was carried out. The linear 38-57 hCGbeta peptide and the corresponding cyclic disulphide peptide were synthesized and antipeptide antibodies developed. Binding studies with antibodies to the linear peptide, and with hCGbeta, hCG and human LH suggest that part of the region is buried at the alpha/beta interface and part exposed in hCG. Observation of the surface exposure of residues 47-53 from the crystal structure of hCG was confirmed by epitope mapping studies of the region. The region is not unique to hCG as a majority of the antibodies to both the linear and cyclic peptides did not exhibit the required specificity. Competitive inhibition studies with the linear and cyclic peptides failed to show inhibition of radiolabelled hCG binding to its receptors. However, both the antipeptide antibodies were able to bioneutralize the hormone in an in vivo assay. Taken together, these results seem to indicate that the L2beta long-loop region is not a receptor-binding site of hCG but spatially close to it.

Analysis of Variance↗
PubMed2001

Mapping the receptor binding regions of human chorionic gonadotropin (hCG) using disulfide peptides of its beta-subunit: possible involvement of the disulfide bonds Cys(9)-Cys(57) and Cys(23)-Cys(72) in receptor binding of the hormone.

Human chorionic gonadotropin (hCG) is a heterodimeric glycoprotein hormone essential for the establishment and maintenance of pregnancy. The alpha- and beta-subunits of hCG are highly cross-linked internally by disulfide bonds which seem to stabilize the tertiary structures required for the noncovalent association of the subunits to generate hormonal activity. The purpose of this study was to delineate the role of the disulfide bonds of hCGbeta in receptor binding of the hormone. Six disulfide peptides incorporating each of the six disulfide bonds of hCGbeta were synthesized and screened, along with their linear counterparts, for their ability to competitively inhibit the binding of [125I] hCG to sheep ovarian corpora luteal LH/CG receptor. Disulfide peptide Cys (9-57) was found to be approximately 4-fold more potent than the most active of its linear counterparts in inhibiting radiolabeled hCG from binding to its receptor. Similarly, disulfide peptide Cys (23-72) exhibited receptor binding inhibition activity, whereas the constituent linear peptides were found to be inactive. The results suggest the involvement of the disulfide bonds Cys(9)-Cys(57) and Cys(23)-Cys(72) of the beta-subunit of hCG in receptor binding of the hormone. This study is the first of its kind to use disulfide peptides rather than linear peptides to map the receptor binding regions of hCG.

Amino Acid Sequence↗
PubMed2000

Constraints in the development of contraceptives for men.

Considerable efforts have been made to develop a male contraceptive and the studies have provided very useful information in this field. At least five different strategies to develop a male contraceptive have been pursued, namely: inhibition of sperm production, interference with sperm function, interruption of sperm transport, prevention of sperm deposition, and prevention of sperm-egg interaction. Of all these approaches, inhibition of sperm production by using androgens either alone or in combination with progestins have given the most encouraging results. A number of clinical trials substantiate that it is indeed possible to have a reversible, effective and safe hormonal method of contraception. A postmeiotic and epididymal approach to interfere with sperm function or the secretory and metabolic processes of the epididymis is another attractive option of male contraceptive development. A number of chemical compounds have been identified which interfere with sperm function in the epididymis without affecting sperm production, however, the compounds evaluated so far were found to be toxic. Interruption of sperm transport through the vas either by vasectomy or percutaneous intravasal injection of liquids which form cure-in-place plugs is also an attractive option. However, reversibility of the methods is of concern in their wide scale use. The major constraint in developing a long-acting male contraceptive seems to be the need for greater investment for product development. The clinical trials for evaluating the efficacy and safety of the new products and formulations stretch over several years and require enormous financial commitment. Nevertheless, the long-term gain of having a long-acting reversible contraceptive for men is far greater than the financial commitments over few years. Male attitude towards using methods of family planning is much more favourable than originally believed. The pharmaceutical industry as well as the health care providers therefore have a greater responsibility. For early development of a contraceptive for men, it is essential to increase investment and simplify the drug regulatory procedures. The advent of newer technologies coupled with the convergent efforts of scientists will certainly make it possible to have an effective, safe and reversible male contraceptive in the near future.

Contraception↗
PubMed1999

Significant intraoperative right ventricular outflow gradients after repair for tetralogy of Fallot: to revise or not to revise?

BACKGROUND: This study was performed to define alternative parameters for the management of intraoperative residual right ventricular outflow obstruction (RVOTO) after transatrial repair of tetralogy of Fallot (ToF) in order to differentiate those requiring immediate revision from those who do not. METHODS: Since October 1995, 166 patients of ToF underwent transatrial repair. Postbypass residual RVOTO was assessed by surgeon's subjective impression, direct intracardiac pressure measurements, and intraoperative echocardiography (IOE). RVOTO was labeled "significant" whenever it exceeded a gradient of 40 mm Hg on IOE or right ventricular to left ventricular pressure ratio (pRV/LV) exceeded 0.85. Further, on IOE, significant RVOTO was defined "fixed", if there was no change in RVOT dimensions during the cardiac cycle, along with the presence of anatomic substrate for obstruction, and "dynamic" if RVOT dimensions increased appreciably in diastole. Postoperative course and follow-up echocardiograms of all patients were analyzed. RESULTS: Significant RVOTO was detected in 58 (35%) patients (mean gradient 54 mm Hg). Seven (12%) of them with fixed obstruction (mean 46 mm Hg) underwent immediate surgical revision, while the remaining 51 patients with mean gradient of 78 mm Hg (including 10 patients with pRV/LV ratio of > or = 1.0) with dynamic obstruction did not undergo revision. There were six (3.6%) early deaths. Operative mortality and postoperative morbidity were not related to higher residual gradients, although the first 15 such patients had longer intensive care stay and inotropic support, in which this was done electively. On follow-up (mean 18.5 months), outflow gradients declined sharply (mean 16 mm Hg) irrespective of the severity of intraoperative gradients (p < 0.001). There were no reoperations or late deaths. CONCLUSIONS: This study shows that: 1) existing parameters for immediate revision of residual RVOTO possibly need to be reviewed; 2) intraoperative echocardiography helps in differentiating "fixed" from "dynamic" obstruction and helps obviate needless revisions; and 3) dynamic RVOT gradients decline significantly irrespective of their severity after transatrial repair of ToF.

Adolescent↗
PubMed1998

Isolation and purification of an early pregnancy factor-like molecule from culture supernatants obtained from lymphocytes of pregnant women.

PURPOSE: Our purpose was to determine whether lymphocytes synthesize proteins during pregnancy, to observe whether one of the proteins synthesized has early pregnancy factor (EPF)-like activity and to isolate and purify this molecule from culture supernatants obtained from stimulated lymphocytes of pregnant women. METHODS: Lymphocyte proliferation assay and 35S-methionine labeling were done to study de novo synthesis of proteins followed by autoradiography to confirm synthesis of proteins. The rosette inhibition assay was used for detection of the EPF-like molecule. Gel filtration on Sephadex G-100 and RPHPLC were used for purification of the EPF-like molecule. RESULTS: The rate of incorporation of 35S-methionine was significantly higher in the lymphocytes of pregnant women compared to those of the control, and autoradiography confirmed the synthesis of proteins during pregnancy. There is a total protein enhancement trend observed during the first trimester that declines toward term. The EPF-like molecule is observed to be synthesized during all the trimesters of pregnancy. This molecule, when purified, showed a single homogeneous biologically active peak. CONCLUSIONS: The results indicated that there is an enhancement of existing protein or synthesis of new proteins during pregnancy. The EPF-like molecule is one of the many proteins synthesized and secreted by lymphocytes during pregnancy that, when purified, is biologically active.

Autoradiography↗
PubMed1997

Identification of bioneutralization epitopes of human follicle stimulating hormone in the regions 31-52 and 66-75 of its beta-subunit.

The crucial role played by follicle stimulating hormone (FSH) in regulating both male and female reproduction and the possibilities of developing contraceptive methods for males by blocking the function of the hormone, makes it important to delineate the hormone-specific bioneutralization epitopes of human follicle stimulating hormone (hFSH) on its beta-subunit. Predictive methods were used to identify the potential surface-oriented regions of hFSH-beta. Peptides corresponding to these regions, i.e. 31-52, 66-75 and 86-95 hFSH-beta, were synthesized, anti-peptide antibodies were elicited in rabbits and the properties of these antisera to bind hFSH and neutralize its biological activity were assessed. Anti-31-52 hFSH-beta antisera bound hFSH specifically, whereas anti-66-75 and anti-86-95 hFSH-beta antisera did not show any detectable binding, proving the region 31-52 hFSH-beta to be a specific antigenic determinant of hFSH. The bioneutralizing abilities of the anti-peptide antibodies were assessed by measuring the hFSH-induced progesterone secretion by rat granulosa cells in vitro. Antibodies to 31-52 and 66-75 hFSH-beta neutralized the bioactivity of hFSH, but anti-86-95 hFSH-beta antibodies did not. Furthermore, the three linear peptides and two disulphide looped peptides of 31-52 hFSH-beta and 86-95 hFSH-beta were also subjected to the in-vitro granulosa cell assay. The linear peptides 31-52 hFSH-beta and 66-75 hFSH-beta and the cyclic 31-52 hFSH-beta disulphide loop peptide significantly inhibited the hFSH-induced progesterone secretion by rat granulosa cells, but the linear 86-95 hFSH-beta peptide and the corresponding cyclic disulphide loop peptide did not. The results clearly show that the regions 31-52 and 66-75 of hFSH-beta harbor bioneutralization epitopes of the hormone. The studies also indicate that cyclization of the linear 31-52 hFSH-beta peptide greatly enhances receptor recognition and that the region 66-75 hFSH-beta may also be involved in hormone-receptor interaction.

Amino Acid Sequence↗
PubMed1996

Comparison of antibodies raised against the peptide 10-24 of chicken riboflavin carrier protein (cRCP) by classical and multiple antigen peptide (MAP) approaches.

Riboflavin carrier protein is an essential protein required for the growth and development of the embryo and hence for the maintenance of pregnancy. Our efforts to delineate the antigenic determinants of chicken riboflavin carrier protein (cRCP) resulted in the identification of a bioneutralization epitope in the region 10-24 of cRCP. The present work compares the properties of the antibodies raised against the peptide epitope by classical and multiple antigen peptide (MAP) system approaches. The extent of cross-reaction of the antibodies to the MAP construct with the parent protein was found to be significantly less as compared to the antibodies raised against the peptide-diphtheria toxoid conjugate. Furthermore, the bioneutralizing ability of the antisera to the MAP construct was also found to be very poor. The results suggest that there are serious limitations in the ability of antibodies raised against MAP constructs to cross-react with the native proteins.

Amino Acid Sequence↗
PubMed1996

Surgical experience with total correction of tetralogy of Fallot in infancy.

Fifty two patients less than one year old with tetralogy of Fallot underwent primary repair between January 1991 and December 1994. Age range was three to twelve months (mean 10.09 +/- 2.01 months) and body weight ranged from 4.5 to 9 kg (mean 8.38 +/- 2.79 kg). Transatrial-transpulmonary repair was performed in 36 patients and the classical transventricular approach was used in 16 patients. Six patients underwent emergency surgery for severe cyanosis and spells. Five patients had left pulmonary artery plasty for pulmonary artery bifurcation stenosis and two out of the five patients who had anomalous coronary arteries needed a right ventricle to pulmonary artery conduit. Mean post repair peak right ventricular/systemic pressure ratio was 0.74 +/- 0.18 in the transventricular group and 0.71 +/- 0.26 in the transatrial-transpulmonary group. There were three hospital deaths. Follow-up ranged from 3 to 46 months (mean 21.18 months). Forty patients underwent echocardiography and twenty patients underwent cardiac catheterisation six to eighteen months after surgery. Mean right ventricular outflow tract gradient on echocardiography was 20.35 +/- 10.12 and, at cardiac catheterisation, 17.51 +/- 13.49 mmHg with mean post repair peak right ventricle/left ventricle pressure ratio of 0.44 +/- 0.11. These were significantly less than the values obtained in the operating room. Only one patient had residual ventricular septal defect with left to right shunt of 1.6:1 at cardiac recatheterisation. There was one late death after reoperation for residual obstruction. Encouraging results with primary repair of tetralogy of Fallot in infancy prompt us to continue this policy in suitable cases.

Body Weight↗
PubMed1996

Regulation of follicular maturation by human ovarian follicular fluid peptide.

Follicular development, ovulation and luteal function are controlled by gonadotrophins. However, recent evidence indicates that local factors are also responsible for the regulation of folliculogenesis. In addition to their endocrine action on pituitary gonadotrophins, inhibin, activin and follistatin also have a paracrine role in follicular maturation. An ovarian follicular fluid peptide (OFFP) has been identified from sheep and humans. Purification of OFFP has been achieved by ultrafiltration and gel chromatography with further purification by fast performance liquid chromatography and reversed phase-high pressure liquid chromatography. OFFP is a small (< 5 kDa) peptide that competes with FSH in binding to granulosa cells in vitro and inhibits progesterone secretion from granulosa cells in culture. Immunohistochemical localization revealed the presence of OFFP mainly in granulosa cells of ovarian follicles. Furthermore, the peptide caused apoptosis in granulosa cells and induced follicular atresia. OFFP may act indirectly on oocytes via its effect on granulosa cells. The peptide from ovarian follicular fluid appears to have an important autocrine or paracrine role in the regulation of folliculogenesis.

Animals↗
PubMed1995

Polymerization of hemoglobin S. Quinary interactions of Glu-43(beta).

Hemoglobin S (HbS) Hoshida and three substituted forms of HbS Hoshida (the substituents being on the amide nitrogen of Gln-43(beta) have been prepared by the amidation of Glu-43(beta) of HbS with ammonia, methylamine, glycine ethyl ester, and galactosamine. The O2 affinity of HbS is increased slightly on amidation of Glu-43(beta). All the four amidated derivatives exhibited nearly the same oxygen affinity. On the other hand, the influence of amidation on the solubility exhibits some sensitivity to the chemical nature of the substituent on the Gln-43(beta). The solubility of HbS Hoshida (a case with no substitution on Gln-43(beta), and the methyl-substituted derivatives are about 33 and 36% higher than that of HbS. The solubility of the HbS modified with the glycine ethyl ester or galactosamine is increased to 41 and 47%, respectively. The first derivative UV spectra of HbS Hoshida and its methyl derivative reflect very little perturbations in their alpha 1 beta 2 interface as compared with that of HbS, whereas the amidated derivatives with larger substituents on Gln-43(beta) reflected noticeable difference. Thus, the increase in the solubility and the oxygen affinity of HbS on the amidation of Glu-43(beta) is primarily a consequence of the loss of the negative charge at 43(beta), a residue proximal to the alpha 1 beta 2 interface. The copolymerization studies of amidated HbS with HbA, and HbS with amidated HbA demonstrate that cis Glu-43(beta) is the "active" residue. This assignment is discrepant with the earlier implication of a trans configuration for this residue in the polymer (Edelstein, S. J. (1981) J. Mol. Biol. 150, 557-575). However, it is consistent with the solution studies of Nagel et al. (Nagel, R. L., Bookchin, R. M., Johnson, J., Labie, D., Wajcman, H.., Isaac-Sodeye, W. A., Honig, G. R., Schiliro, G., Crookstan, J. H., and Matsutomo, K. (1979) Proc. Nat. Acad. Sci. U.S.A. 76, 670-672) and McCurdy et al. (McCurdy, P. R., Lorkin, P. A., Casey, R., Lehmann, H., Uddin, D. E., and Dickson, L. G. (1974) Am. J. Med. 57, 665-760).

Adult↗