Novel Nad-Binding in Aldehyde Dehydrogenase - A New Twist on an Old Theme. Zhi-Jie Liu1, John Rose1, John Hempel2, Ronald Lindhal3 and Bi-Cheng Wang1, 1Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, U.S.A., 2Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15219, U.S.A. and 3Department of Biochemistry and Molecular Biology, University of South Dakota, Vermillion, SD 57069, U.S.A.
The Gly-X-Gly-X-X-Gly motif, a "fingerprint" sequence known for identifying the dinucleotide-binding domain in nicotinamide adenine dinucleotide (NAD)-dependent dehydrogenases, is found at the N-terminus of a-helix A (aA) of the "Rossmann fold" in most dehydrogenases. However in aldehyde dehydrogenase (ALDH) a "Gly-X-X-X-X-Gly" segment is instead found near the N-terminus of a-helix D (aD) of the "Rossmann fold". In response to this, the pyrophosphate group of NAD in ALDH moves away from the N-terminus of aA and is located in proximity to, but not directly at, the N-terminus of aD. This enables the nicotinamide ring of NAD to sandwich between two strictly conserved residues, Phe-335 and Gly-187. The latter is the first glycine in the Gly-X-X-X-X-Gly sequence. The adenine ring of NAD is buried inside a hydrophobic pocket, formed by 7 residues from [beta]1, aC and aD. Despite this significantly altered mode of NAD binding within the "Rossmann fold", the adenine ribose forms two hydrogen bonds with an acidic residue (Glu-140) at the C-terminus of [beta]2 similar to other NAD-dependent dehydrogenases. Thus, the NAD-binding motif in ALDH is a [beta]-a,[beta] structure, instead of the established [beta]-a-[beta] motif observed in the 11 other families of NAD-dependent dehydrogenases. A correlation of three-dimensional structure with amino acid sequences from other ALDHs as well as other oxidoreductases suggests that this novel NAD-binding mode is the norm for all members of ALDH family, representing a new mode of NAD-binding.
Work supported by a grant AA06985 from the National Institute of Alcohol Abuse and Alcoholism