The C-terminal region of human angiogenin has a dual role in enzymatic activity.
The ribonucleolytic activity of angiogenin (Ang) is essential to Ang's capacity to induce blood vessel formation. Previous x-ray diffraction and mutagenesis results have shown that the active site of the human protein is obstructed by Gln-117 and imply that the C-terminal region of Ang must undergo a conformational rearrangement to allow substrate binding and catalysis. As a first step toward structural characterization of this conformational change, additional site-directed mutagenesis and kinetic analysis have been used to examine the intramolecular interactions that stabilize the inactive conformation of the protein. Two residues of this region, Ile-119 and Phe-120, are found to make hydrophobic interactions with the remainder of the protein and thereby help to keep Gln-117 in its obstructive position. Furthermore, the suppression of activity by the intramolecular interactions of Ile-119 and Phe-120 is counterbalanced by an effect of the adjacent residues, Arg-121, Arg-122, and Pro-123 which do not appear to form contacts with the rest of the protein structure. They contribute to enzymatic activity, probably by constituting a peripheral subsite for binding polymeric substrates. The results reveal the nature of the conformational change in human Ang and assign a key role to the C-terminal region both in this process and, presumably, in the regulation of human Ang function.
Russo
N
N
Center for Biochemical and Biophysical Sciences and Medicine, Harvard Medical School, Boston, MA 02115, USA.
Nobile
V
V
Di Donato
A
A
Riordan
J F
JF
Vallee
B L
BL
D000595:Amino Acid Sequence; D043925:Angiogenesis Inducing Agents / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D000432:Methanol / Q000494:pharmacology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012259:Ribonuclease, Pancreatic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D043925:Angiogenesis Inducing Agents; D011506:Proteins; D011994:Recombinant Proteins; C046366:angiogenin; D012259:Ribonuclease, Pancreatic; D000432:Methanol