Boon Elizabeth M, Davis Joseph H, Tran Rosalie, Karow David S, Huang Shirley H, Pan Duohai, Miazgowicz Michael M, Mathies Richard A, Marletta Michael A
Department of Chemistry, University of California, Berkeley, California 94720.
Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, Michigan 48109.
J Biol Chem. 2006 Aug 4;281(31):21892-21902. doi: 10.1074/jbc.M600557200. Epub 2006 May 25.
The heme cofactor in soluble guanylate cyclase (sGC) is a selective receptor for NO, an important signaling molecule in eukaryotes. The sGC heme domain has been localized to the N-terminal 194 amino acids of the beta1 subunit of sGC and is a member of a family of conserved hemoproteins, called the H-NOX family (Heme-Nitric Oxide and/or OXygen-binding domain). Three new members of this family have now been cloned and characterized, two proteins from Legionella pneumophila (L1 H-NOX and L2 H-NOX) and one from Nostoc punctiforme (Np H-NOX). Like sGC, L1 H-NOX forms a 5-coordinate Fe(II)-NO complex. However, both L2 H-NOX and Np H-NOX form temperature-dependent mixtures of 5- and 6-coordinate Fe(II)-NO complexes; at low temperature, they are primarily 6-coordinate, and at high temperature, the equilibrium is shifted toward a 5-coordinate geometry. This equilibrium is fully reversible with temperature in the absence of free NO. This process is analyzed in terms of a thermally labile proximal Fe(II)-His bond and suggests that in both the 5- and 6-coordinate Fe(II)-NO complexes of L2 H-NOX and Np H-NOX, NO is bound in the distal heme pocket of the H-NOX fold. NO dissociation kinetics for L1 H-NOX and L2 H-NOX have been determined and support a model in which NO dissociates from the distal side of the heme in both 5- and 6-coordinate complexes.
可溶性鸟苷酸环化酶（sGC）中的血红素辅因子是一氧化氮（NO）的选择性受体，NO是真核生物中一种重要的信号分子。sGC血红素结构域定位于sGC β1亚基的N端194个氨基酸，是一个保守的血红素蛋白家族（称为H-NOX家族，即血红素-一氧化氮和/或氧结合结构域）的成员。该家族现已克隆并鉴定出三个新成员，分别是嗜肺军团菌的两种蛋白（L1 H-NOX和L2 H-NOX）以及点状念珠藻的一种蛋白（Np H-NOX）。与sGC一样，L1 H-NOX形成五配位的Fe(II)-NO复合物。然而，L2 H-NOX和Np H-NOX均形成五配位和六配位Fe(II)-NO复合物的温度依赖性混合物；在低温下，它们主要是六配位的，而在高温下，平衡向五配位几何结构移动。在没有游离NO的情况下，这种平衡随温度完全可逆。根据热不稳定的近端Fe(II)-His键对这一过程进行了分析，表明在L2 H-NOX和Np H-NOX的五配位和六配位Fe(II)-NO复合物中，NO均结合在H-NOX折叠结构的远端血红素口袋中。已测定了L1 H-NOX和L2 H-NOX的NO解离动力学，并支持一个模型，即NO在五配位和六配位复合物中均从血红素的远端解离。
