Binding of phosphate and pyrophosphate ions at the active site of human angiogenin as revealed by X-ray crystallography

Dd. Leonidas et al., Binding of phosphate and pyrophosphate ions at the active site of human angiogenin as revealed by X-ray crystallography, PROTEIN SCI, 10(8), 2001, pp. 1669-1676
Citations number
Categorie Soggetti
Biochemistry & Biophysics
Journal title
ISSN journal
0961-8368 → ACNP
Year of publication
1669 - 1676
SICI code
Human angiogenin (Ang) is an unusual homolog of bovine pancreatic RNase A t hat utilizes its ribonucleolytic activity to induce the formation of new bl ood vessels. The pyrimidine-binding site of Ang was shown previously to be blocked by glutamine 117, indicating that Ang must undergo a conformational change to bind and cleave RNA. The mechanism and nature of this change are not known, and no Ang-inhibitor complexes have been characterized structur ally thus far. Here, we report crystal structures for the complexes of Ang with the inhibitors phosphate and pyrophosphate, and the structure of the c omplex of the superactive Ang Variant Q117G with phosphate, all at 2.0 Angs trom resolution. Phosphate binds to the catalytic site of both Ang and Q117 G in essentially the same manner observed in the RNase A-phosphate complex, forming hydrogen bonds with the side chains of His 13, His 114, and Gln 12 , and the main chain of Leu 115; it makes an additional interaction with th e Lys 40 ammonium group in the Ang complex. One of the phosphate groups of pyrophosphate occupies a similar position. The other phosphate extends towa rd Gin 117, and lies within hydrogen-bonding distance from the side-chain a mide of this residue as well as the imidazole group of His 13 and the main- chain oxygen of Leu 115. The pyrimidine site remains obstructed in all thre e complex structures, that is, binding to the catalytic center is not suffi cient to trigger the conformational change required for catalytic activity, even in the absence of the Gin 117 side chain. The Ang-pyrophosphate compl ex structure suggests how nucleoside pyrophosphate inhibitors might bind to Ang; this information may be useful for the design of Ang antagonists as p otential anti-angiogenic drugs.