Crystal Structure of CYP105A1 (P450SU-1) in Complex with 1 alpha ,25-Dihydroxyvitamin D sub(3)

• Published in: Biochemistry (Easton) Vol. 47; no. 13; pp. 4017 - 4027
• Main Authors: Kamakura, Masaki, Sakaki, Toshiyuki, Hayashi, Keiko, Shinkyo, Raku, Yamada, Masato, Shiro, Yoshitsugu, Ikushiro, Shin-ichi, Sugimoto, Hiroshi, Yoneda, Sachiyo
• Format: Journal Article
• Language: English
• Published: 01.01.2008
• Subjects: Streptomyces griseolus
• ISSN: 0006-2960
• DOI: 10.1021/bi7023767

Vitamin D sub(3) (VD sub(3)), a prohormone in mammals, plays a crucial role in the maintenance of calcium and phosphorus concentrations in serum. Activation of VD sub(3) requires 25-hydroxylation in the liver and 1 alpha - hydroxylation in the kidney by cytochrome P450 (CYP) enzymes. Bacterial CYP105A1 converts VD sub(3) into 1 alpha ,25-dihydroxyvitamin D sub(3) (1 alpha ,25(OH) sub(2)D sub(3)) 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 1 alpha ,25(OH) sub(2)D sub(3). The compound 1 alpha ,25(OH) sub(2)D sub(3) is positioned 11 Aa from the iron atom along the I helix within the pocket. A similar binding mode is observed in the structure of the human CYP2R1-VD sub(3) 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 1 alpha -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 VD sub(3).