C-Terminal end and aminoacid Lys48 in HMG-CoA lyase are involved in substrate binding and enzyme activity

3-Hydroxy-3-methylglutaryl-CoA (HMG-CoA) lyase adopts a (βα)8 TIM barrel structure with an additional β9, α11 and α12 helices. Location of HMG part of the substrate has been suggested but the binding mode for the CoA moiety remains to be resolved. As mutation F305 fs(−2), which involves the last 21 residues of the protein, and mutation K48N caused 3-hydroxy-3-methylglutaric aciduria in two patients, we examined the role of the C-terminal end and Lys48 in enzyme activity. Expression studies of various C-terminal-end-deleted and K48N-mutated proteins revealed that residues 311--313 (localized in the loop between α11 and α12 helices) and Lys48 are essential for enzyme activity. An in silico docking model locating HMG-CoA on the surface of the enzyme implicates Asn311 and Lys313 in substrate binding by establishing multiple polar contacts with phosphate and ribose groups of adenosine, and Lys48 by contacting the carboxyl group of the panthotenic acid moiety.