C David Stout — Page 3

PubMed2002

The structure of microsomal cytochrome P450 2C5: a steroid and drug metabolizing enzyme.

The structure of microsomal P450 2C5 is the first structure of a membrane P450 to be determined by x-ray diffraction. This enzyme was originally identified as a progesterone 21-hydroxylase that is polymorphically expressed in rabbit liver. In contrast to the adrenal 21-hydroxylase, P450 2C5 metabolizes structurally diverse substrates that include a variety of steroids as well as therapeutic drugs. The flexible architecture of the enzyme and the residual solvation of the substrate provide a basis for understanding the catalytic diversity of 2C5 and related drug metabolizing P450s. In addition, the structure of P450 2C5 suggests how mammalian P450s have adapted for membrane binding and interaction with microsomal P450 reductase.

Animals↗

PubMed2001

Azotobacter vinelandii ferredoxin I: a sequence and structure comparison approach to alteration of [4Fe-4S]2+/+ reduction potential.

The reduction potential (E(0)') of the [4Fe-4S](2+/+) cluster of Azotobacter vinelandii ferredoxin I (AvFdI) and related ferredoxins is approximately 200 mV more negative than the corresponding clusters of Peptostreptococcus asaccharolyticus ferredoxin and related ferredoxins. Previous studies have shown that these differences in E(0)' do not result from the presence or absence of negatively charged surface residues or in differences in the types of hydrophobic residues found close to the [4Fe-4S](2+/+) clusters. Recently, a third, quite distinct class of ferredoxins (represented by the structurally characterized Chromatium vinosum ferredoxin) was shown to have a [4Fe-4S](2+/+) cluster with a very negative E(0)' similar to that of AvFdI. The observation that the sequences and structures surrounding the very negative E(0)' clusters in quite dissimilar proteins were almost identical inspired the construction of three additional mutations in the region of the [4Fe-4S](2+/+) cluster of AvFdI. The three mutations, V19E, P47S, and L44S, that incorporated residues found in the higher E(0)' P. asaccharolyticus ferredoxin all led to increases in E(0)' for a total of 130 mV with a 94-mV increase in the case of L44S. The results are interpreted in terms of x-ray structures of the FdI variants and show that the major determinant for the large increase in L44S is the introduction of an OH-S bond between the introduced Ser side chain and the Sgamma atom of Cys ligand 42 and an accompanying movement of water.

Amino Acid Sequence↗