Comparative kinetics of cofactor association and dissociation for the human and trypanosomal S-adenosylhomocysteine hydrolases., 2: The role of helix 18 stability

BIOL 27

Qingshan Li1, Sumin Cai2, Jianwen Fang3, Ronald T. Borchardt, rborchardt@ku.edu1, Krzysztof Kuczera, kkuczera@ku.edu4, C. Russell Middaugh, middaugh@ku.edu1, and Richard L. Schowen, rschowen@ku.edu1. (1) Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Avenue, Lawrence, KS 66047, (2) Department of Molecular Biosciences, University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66045, (3) Bioinformatics Core Facility, University of Kansas, 2121 Simons Drive, Lawrence, KS 66047, (4) Departments of Chemistry and Molecular Biosciences, University of Kansas, 1251 Wescoe Hall Dr, Lawrence, KS 66045
Binding of NAD(H) in S-adenosyl-L-homocysteine hydrolases (SAHH) from human (Hs-SAHH) and parasites requires direct contributions from two residues of a neighbor subunit: a Lys and a Tyr close to C-terminus and linked to helix 18 via several residues. Estimation by helix propensity, helices 18 of Hs-SAHH and SAHH from Plasmodium falciparum (Pf-SAHH) are the most stable and unstable ones among the four SAHHs including another two parasitic enzymes from Trypanosoma cruzi (Tc-SAHH) and Leishmania donovani, respectively. Replacement with helix 18 from Hs-SAHH, the Tc-SAHH mutant did not change much of its catalytic properties, but significantly increased NAD+ association rate and decreased NAD+ dissociation rate at high temperature. On the other side, replacement with helix 18 from Pf-SAHH, the Hs-SAHH mutant did not significantly change its catalytic properties either, but showed weaker NAD+ association and faster dissociation at high temperature. The stability of helix 18 significantly influences the cofactor binding.
 

Frontiers in Chemical Biology
5:00 PM-7:00 PM, Sunday, August 19, 2007 BCEC -- Exhibit Hall - B2, Poster

Division of Biological Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007