Structure and Function of Peptide and Protein Hormones

Child Health And Human Development

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Abstract

This research program is concerned with the analysis, synthesis, protein expression, and structure-function relationships of peptide and protein hormones. Current emphases are placed on the structure and function of the angiotensin II (AngII) and gonadotropin-releasing hormone (GnRH) receptors. In collaborative research projects, identification of phosphorylation sites by protein kinases, and of gene sequences differing antineurogenic effects of transcription factors in Xenopus, were undertaken. Accomplishments of these projects include: (1) Mutational analysis of the amino acid residues in the sequence KPRNDDIFR in position 232-240 of the third cytoplasmic loop of the rat Type 1a AngII receptor Type 1a revealed that agonist activation of the receptor is dependent on two adjacent apolar residues, Ile at position 238 and Phe at position 239. This Ile residues also appears to be required for the activation of other G protein-coupled receptors by their agonist ligands. (2) Antisera were raised against a mouse GnRH receptor fragment, residues 232-298, expressed in E. coli as a maltose-binding protein fusion protein. Immunostaining with these antisera permitted the detection of GnRH receptor expression showing a typical bipolar morphology in cultured fetal hypothalamic neurons and rat E12 olfactory placode cells. (3) Protein sequence analysis has identified a chromosomal nonhistone high-mobility-group protein (HMG-1) that binds the AT-rich sequence within the promoters of the brain-specific protein kinase C (PKC)-gamma and neurogranin/RC3 genes. Phosphorylation sites on HMG-1 by PKC-gamma and cdc2 kinase that attenuate varied degrees of DNA binding activity were also identified. (4) Chimeric studies of Xenopus erythroid transcription factor GATA-1a and GATA-1b genes revealed that the sequence variations in their coding region do not account for their differing non-erythroidal function, namely anti-neurogenesis during embryonic development. The sequence in the 3'-untranslated region of GATA-1b, but not that of GATA-1a, is essential for the anti-neurogenic effect.