Flinspach Mack L, Li Huiying, Jamal Joumana, Yang Weiping, Huang Hui, Hah Jung-Mi, Gómez-Vidal José Antonio, Litzinger Elizabeth A, Silverman Richard B, Poulos Thomas L
Department of Molecular Biology and Biochemistry and the Program in Macromolecular Structure, University of California, Irvine, California 92697-3900, USA.
Nat Struct Mol Biol. 2004 Jan;11(1):54-9. doi: 10.1038/nsmb704. Epub 2003 Dec 29.
Three nitric oxide synthase (NOS) isoforms, eNOS, nNOS and iNOS, generate nitric oxide (NO) crucial to the cardiovascular, nervous and host defense systems, respectively. Development of isoform-selective NOS inhibitors is of considerable therapeutic importance. Crystal structures of nNOS-selective dipeptide inhibitors in complex with both nNOS and eNOS were solved and the inhibitors were found to adopt a curled conformation in nNOS but an extended conformation in eNOS. We hypothesized that a single-residue difference in the active site, Asp597 (nNOS) versus Asn368 (eNOS), is responsible for the favored binding in nNOS. In the D597N nNOS mutant crystal structure, a bound inhibitor switches to the extended conformation and its inhibition of nNOS decreases >200-fold. Therefore, a single-residue difference is responsible for more than two orders of magnitude selectivity in inhibition of nNOS over eNOS by L-N(omega)-nitroarginine-containing dipeptide inhibitors.
三种一氧化氮合酶（NOS）亚型，即内皮型一氧化氮合酶（eNOS）、神经元型一氧化氮合酶（nNOS）和诱导型一氧化氮合酶（iNOS），分别产生对心血管系统、神经系统和宿主防御系统至关重要的一氧化氮（NO）。开发亚型选择性NOS抑制剂具有相当大的治疗意义。解析了与nNOS和eNOS复合的nNOS选择性二肽抑制剂的晶体结构，发现这些抑制剂在nNOS中呈卷曲构象，而在eNOS中呈伸展构象。我们推测，活性位点中的单个残基差异，即天冬氨酸597（nNOS）与天冬酰胺368（eNOS），是导致在nNOS中更有利结合的原因。在D597N nNOS突变体晶体结构中，结合的抑制剂转变为伸展构象，其对nNOS的抑制作用降低了200倍以上。因此，单个残基差异导致含L-N（ω）-硝基精氨酸的二肽抑制剂对nNOS的抑制选择性比对eNOS高两个数量级以上。
