Crystal Structure of CYP105A1 (P450SU-1) in Complex with 1α,25-Dihydroxyvitamin D3

• Published in: Biochemistry (Easton) Vol. 47; no. 13; pp. 4017 - 4027
• Main Authors: Sugimoto, Hiroshi, Shinkyo, Raku, Hayashi, Keiko, Yoneda, Sachiyo, Yamada, Masato, Kamakura, Masaki, Ikushiro, Shin-ichi, Shiro, Yoshitsugu, Sakaki, Toshiyuki
• Format: Journal Article
• Language: English
• Published: American Chemical Society 01.04.2008
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi7023767

Vitamin D3 (VD3), a prohormone in mammals, plays a crucial role in the maintenance of calcium and phosphorus concentrations in serum. Activation of VD3 requires 25-hydroxylation in the liver and 1α-hydroxylation in the kidney by cytochrome P450 (CYP) enzymes. Bacterial CYP105A1 converts VD3 into 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) in two independent reactions, despite its low sequence identity with mammalian enzymes (<21% identity). The present study determined the crystal structures of a highly active mutant (R84A) of CYP105A1 from Streptomyces griseolus in complex and not in complex with 1α,25(OH)2D3. The compound 1α,25(OH)2D3 is positioned 11 Å from the iron atom along the I helix within the pocket. A similar binding mode is observed in the structure of the human CYP2R1−VD3 complex, indicating a common substrate-binding mechanism for 25-hydroxylation. A comparison with the structure of wild-type CYP105A1 suggests that the loss of two hydrogen bonds in the R84A mutant increases the adaptability of the B′ and F helices, creating a transient binding site. Further mutational analysis of the active site reveals that 25- and 1α-hydroxylations share residues that participate in these reactions. These results provide the structural basis for understanding the mechanism of the two-step hydroxylation that activates VD3.