The research program of the Unit on Molecular Structure and Protein Chemistry is concerned with the analysis, synthesis, protein expression, and structure-function relationships of peptide and protein hormones. Current work focuses on the structure and function of the angiotensin II (Ang II) and gonadotropin-releasing hormone (GnRH) receptors.

Recent accomplishments include synthesis of a rhodamine B conjugate of Ang II at its amino-terminus and of a sulforhodamine 101 (Texas Red) conjugate of [D-Lys⁶, des Gly¹⁰amide]GnRHethyl-amide at e-amino group of D-Lys⁶. Both conjugates are biologically active as revealed on confocal microscopy and by their ability to bind to their receptors and internalize in the same manner as the natural ligands. The unit also developed a method for converting phospho-Ser and phospho-Thr to cysteic acid and beta-methyl cysteic acid, respectively. The stability of the sulfo-moiety over the phospho-moiety for collision-induced dissociation MS/MS peptide sequence analysis during low-energy collision in electron spray ionization was shown to simplify the identification of phosphorylation sites in peptides. The unit also undertook a yeast two-hybrid study using as bait the C-terminal fragment (residues 301-359) of the human AT₁ receptor (hAT1) in which potential phosphorylation sites (Thr^{332, 336} and Ser³³⁵) were mutated to Asp to mimic phosphorylated residues. The investigation yielded one clone corresponding to the MHC class II-associated invariant chain, Ii, from screening of a human kidney cDNA library. Using confocal microscopy, we demonstrated an association of hAT1 and Ii in vivo by yeast mating experiments and by colocalization at the plasma membrane of human embryonic kidney (HEK-293) cells. HEK cells were transfected with both AT₁-green fluorescent protein and Ii-red fluorescent protein fusion proteins. Finally, we demonstrated that, among egg glycoproteins, those from the pigeon are unique in that they possess binding activity for uropathogenic Eschericia coli and Shigella suis. A preparative reverse-HPLC system was devised to isolate four components from pigeon egg white proteins, which were characterized by sequencing and SwissProt homology search, allowing their identification as ovomucoid, ovotransferrin, and two ovalbumins. All four proteins contain a terminal a Gal-alpha1-4Gal sequence that is uncommon in mammals and other avians but is known to facilitate binding to the microbes. Matrix-assisted laser desorption/ionization mass spectrometric analysis revealed pigeon ovomucoid and a high molecular weight albumin to be larger than their chicken counterparts. The differences are attributable to the number and length of their oligosaccharide chains.