Search

G protein-coupled receptors (GPCRs) belonging to class A contain several highly conserved (>90%) amino acids in their transmembrane helices. Results of mutational studies of these highly conserved residues suggest a common mechanism for locking GPCRs in an inactive conformation and for their subsequent activation upon ligand binding. Recently, a second set of sites in the transmembrane helices has been identified in which amino acids with small side chains, such as Gly, Ala, Ser, Thr, and Cys, are highly conserved (>90%) when considered as a group. These group-conserved residues have not been recognized as having essential structural or functional roles. To determine the role of group-conserved residues in the [[beta].sub.2]-adrenergic receptor ([[beta].sub.2]-AR), amino acid replacements guided by molecular modeling were carried out at key positions in transmembrane helices H2-H4. The most significant changes in receptor expression and activity were observed upon replacement of the amino acids Ser-161 and Ser-165 in H4. Substitution at these sites by larger residues lowered the expression and activity of the receptor but did not affect specific binding to the antagonist ligand dihydroalprenolol. A second site mutation, V114A, rescued the low expression of the $165V mutant. Substitution of other group-conserved residues in H2-H4 by larger amino acids lowered receptor activity in the order Ala-128, Ala-76, Ser-120, and Ala-78. Together these data provide comprehensive analysis of group-conserved residues in a class A GPCR and allow insights into the roles of these residues in GPCR structure and function. rhodopsin | G protein-coupled receptors | helix packing | site-directed mutagenesis | molecular modeling

The biochemical and structural characterization of proteolyzed HPII, confirming that the large subunit HPII that can be truncated to a core structure that is similar in many respects to the small subunit clade Mn-containing and 78-84 kDa catalases is reported. It is found that the truncated variant exhibits a 1.8 times faster turnover rate and enhanced sensitivity to high concentrations of H(sub 2)O(sub 2) consistent with easier access of the substrate to the active site.

Results reveal that treatment of hydroperoxidase II with proteases under limited digestion conditions cleave 72-74 residues from the N-terminus of each sububit of the homotetrmer enzyme with 80% of the wild-type activity. Longer treatment of the enzyme with proteinase K removes the C-terminus but yet retains the tetrameric structure with 80% of the wild-type activity.