This laboratory is interested in the relationship between protein sequence, structure and the mechanisms of protein folding and enzymic reactions. (i) Histidine Rich Proteins We have reinvestigated the spectroscopic behaviour of poly L-histidine as a function of pH and solvent additives, and established a set of reference circular dichroism spectra (CD) under defined conditions, which can be used in analysis of the structures of some unusual proteins, produced by malaria parasites. The polypeptide's CD spectrum is found to be a complex function of pH, solvent composition and peptide concentration, which is most easily interpreted by assuming the presence of aggregated forms with specific molecular conformations. (ii) Structure of Tryptophan Synthase (with Dr. Edith Wilson Miles and coworkers, LBP) We are investigating the conformational states of the tryptophan synthase alpha2-beta2 complex and of the separate alpha and beta subunits, using site directed mutagenesis. Alteration of residues known to be at the enzyme's active sites produces drastic changes in both the mechanism and spectrophotometric properties of the protein. (iii) Structure of Mammalian Sulphotransferases. (with Dr. D. Marshall and Dr. W.B. Jakoby, LBM) The enzymatic activity of a phenol sulphotransferase, from rat liver, has been shown to be regulated by reversible oxidation/reduction of a conserved specific cysteine residue by physiological concentrations of glutathione. Oxdation cysteine residue 66 inhibits the physiological activity of the enzyme by very tight substrate inhibition. This mechanism may be important under conditions of oxidative stress to the liver. (iv) Structure of Keratinocyte Growth Factor. (with Dr. D. Bottaro, LCMB, NCI) To identify regions in KGF that contribute to heparin binding, we investigated a series of peptides spanning defined motifs in the predicted structure of the protein. One peptide from the carboxy terminus, which showed binding affinity comparable to intact KGF, was shown to be folded into a ?-hairpin in the presence of the polysaccharide. (v) Interaction of Neurogranin with Calmodulin. (with Dr. K.P. Huang, ERRB, NICHD) In the absence of calcium, neurorgranin forms an inactive complex with calmodulin, which can be detected by an increase in -helical conent of the proteins. The formation of the complex can be regulated by variations in calcium ion concentrations or by oxidation/reduction of a pair of conserved cysteine residues in neurogranin.
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