Alvarez Claudia P, Stagljar Marijana, Muhandiram D Ranjith, Kanelis Voula
Department of Chemical and Physical Sciences, University of Toronto Mississauga , 3359 Mississauga Road, Mississauga, Ontario, Canada L5L 1C6.
Department of Chemistry, University of Toronto , 80 St. George Street, Toronto, Ontario, Canada M5S 3H6.
Biochemistry. 2017 May 9;56(18):2400-2416. doi: 10.1021/acs.biochem.6b00681. Epub 2017 Apr 25.
The sulfonylurea receptor 1 (SUR1) protein forms the regulatory subunit in ATP sensitive K (K) channels in the pancreas. SUR proteins are members of the ATP binding cassette (ABC) superfamily of proteins. Binding and hydrolysis of MgATP at the SUR nucleotide binding domains (NBDs) lead to channel opening. Pancreatic K channels play an important role in insulin secretion. SUR1 mutations that result in increased levels of channel opening ultimately inhibit insulin secretion and lead to neonatal diabetes. In contrast, SUR1 mutations that disrupt trafficking and/or decrease gating of K channels cause congenital hyperinsulinism, where oversecretion of insulin occurs even in the presence of low glucose levels. Here, we present data on the effects of specific congenital hyperinsulinism-causing mutations (G716V, R842G, and K890T) located in different regions of the first nucleotide binding domain (NBD1). Nuclear magnetic resonance (NMR) and fluorescence data indicate that the K890T mutation affects residues throughout NBD1, including residues that bind MgATP, NBD2, and coupling helices. The mutations also decrease the MgATP binding affinity of NBD1. Size exclusion and NMR data indicate that the G716V and R842G mutations cause aggregation of NBD1 in vitro, possibly because of destabilization of the domain. These data describe structural characterization of SUR1 NBD1 and shed light on the underlying molecular basis of mutations that cause congenital hyperinsulinism.
磺脲类受体1（SUR1）蛋白构成胰腺中ATP敏感性钾（K）通道的调节亚基。SUR蛋白是ATP结合盒（ABC）超家族蛋白的成员。在SUR核苷酸结合结构域（NBDs）处MgATP的结合和水解导致通道开放。胰腺K通道在胰岛素分泌中起重要作用。导致通道开放水平增加的SUR1突变最终会抑制胰岛素分泌并导致新生儿糖尿病。相反，破坏K通道转运和/或降低其门控作用的SUR1突变会导致先天性高胰岛素血症，即使在低血糖水平下也会出现胰岛素分泌过多的情况。在此，我们展示了位于第一个核苷酸结合结构域（NBD1）不同区域的特定先天性高胰岛素血症致病突变（G716V、R842G和K890T）的影响数据。核磁共振（NMR）和荧光数据表明，K890T突变影响整个NBD1的残基，包括结合MgATP的残基、NBD2和偶联螺旋。这些突变还降低了NBD1对MgATP的结合亲和力。尺寸排阻和NMR数据表明，G716V和R842G突变在体外导致NBD1聚集，这可能是由于该结构域的不稳定。这些数据描述了SUR1 NBD1的结构特征，并揭示了导致先天性高胰岛素血症的突变的潜在分子基础。
