Peptide induced polymorphism in model membranes.

Lipids in biological membranes generally adopt bilayer structures. However, incorporation of peptides may induce alterations in such structures. We have studied the influence of tryptophan, leucine, Trp-Leu, luteinizing hormone releasing hormone and renin inhibitor peptide on lipid organisation in liposomes. It has been observed that the effect is specific to the peptide molecule as-a whole and does not have direct correlation to the constituent amino acids or the conformation of the molecule.

Magnetic resonance methods for studying intact spermatozoa.

Motility is used as a routine parameter for assessing spermatozoa activity. The quality rating techniques adopted are based on electron or optical microscopy. However, these methods depend on gross structural and dynamical features of sperm cells and do not provide information on metabolic activity of intact cells. Lately, biochemical assays have become popular. Such methods are cumbersome and destroy the samples. Magnetic resonance methods offer a non-invasive method for studies on intact sperms. We have investigated respiration, maturation and in vitro capacitation of sperms from human ejaculates and sperms extracted from goat reproductive organ using electron spin resonance spin labelling and [31P] nuclear magnetic resonance methods. These studies clearly establish the advantages of magnetic resonance in studies related to metabolic activity of sperms.

Refined procedures for accurate determination of solution structures of nucleic acids by two dimensional nuclear magnetic resonance spectroscopy.

New procedures have been described for accurate determination of solution structures of nucleic acids. These are two fold; new two dimensional nuclear magnetic resonance techniques and better approaches for interpretation of nuclear magnetic resonance data for structure determination purposes. The significant development in two dimensional nuclear magnetic resonance techniques for this purpose are ω1 -scaling and recording of pure phase spectra. Use of ω1-scaled correlated and nuclear Overhauser effect spectra for estimation of interproton distances and 1H-1H coupling constants has been described. Computer simulation procedures for exact determination of structure have been described. Experimental spectra demonstrating the application of new procedures have been presented.

Recognition schemes for protein-nucleic acid interactions.

The molecular forces involved in protein-nucleic acid interaction are electrostatic, stacking and hydrogen-bonding. These interactions have a certain amount of specificity due to the directional nature of such interactions and the spatial contributions of the steric effects of different substituent groups. Quantum chemical calculations on these interactions have been reported which clearly bring out such features. While the binding energies for electrostatic interactions are an order of magnitude higher, the differences in interaction energies for structures stabilised by hydrogen-bonding and stacking are relatively small. Thus, the molecular interactions alone cannot explain the highly specific nature of binding observed in certain segments of proteins and nucleic acids. It is therefore logical to assume that the sequence dependent three dimensional structures of these molecules help to place the functional groups in the correct geometry for a favourable interaction between the two molecules. We have carried out 2D-FT nuclear magnetic resonance studies on the oligonucleotide d- GGATCCGGATCC. This oligonucleotide sequence has two binding sites for the restriction enzyme Bam H1. Our studies indicate that the conformation of this DNA fragment is predominantly B-type except near the binding sites where the ribose ring prefers a 3E conformation. This interesting finding raises the general question about the presence of specificity in the inherent backbone structures of proteins and nucleic acids as opposed to specific intermolecular interactions which may induce conformational changes to facilitate such binding.