Substrate selectivities and structure-function relationships of human cytochrome P450 enzymes

Enzymes of the cyto chrome P450 (CYP) superfamil y are responsib le for the meta bolism of a myria d of compounds th at in clu de drugs, non-drug xenobiotics (e.g. environmenta l chemicals), and endogenous compounds. The in div id ual P450 enzymes exhib it characteris tic substr ate and inhib itor selectiv ities, and enzyme activities are varia bly affected by age, dis ease sta te s, epig enetic regulation, eth nic it y, genetic polymorphis m, and hormonal factors. Not surpris ingly, wid e in te rin divid ual varia bility in clearance (and hence response) is ofte n a feature of drugs meta bolised by P450 enzymes. However, knowle dge of th e P450 enzyme(s) responsib le for th e meta bolis m of a compound (‘reaction phenotyping’) allows predic tion, at least at the quali ta ti ve le vel, of factors lik ely to alter clearance in patients . In vitr o approaches for th e reaction phenotyping of P450 substr ate s have been developed in recent years, alt hough th e relia bility of reaction phenotyping is crit ically dependent on experimenta l conditions. Moreover, th e str uctural features of P450 prote in s th at confer substr ate and in hib itor selectivit y, includin g the contr ib ution of individ ual amin o acids to ligand binding, are becomin g increasingly understood from site -dir ected muta genesis , x-ray crysta llography, and prote in homology modelling. While x-ray crysta llographic data provid e valu able insights into P450 substr ate /i nhib itor binding domains, th e str uctures elu cid ated are sta tic and data are li mited in te rms of th e thermodynamic s of bin din g an d movements of indiv id ual amin o acid s. Molecula r dynamic s simula tio ns provid e a means to model th e thermodynamic s and fle xib ility of protein s, and conformational changes can be stu die d in deta il at the ato mic le vel over time. It wil l be demonstr ate d how mole cula r dynamic s simula tions have allowed us to dif ferentiate bin ding modes and key amino acids for acidic (‘ty pic al’ ) and basic (‘atypical’) substr ate s of CYP2C9