Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Biochim Biophys Acta Biomembr. 2017 Dec;1859(12):2420-2434. doi: 10.1016/j.bbamem.2017.09.016. Epub 2017 Sep 21.
The availability of the first crystal structure of a bacterial member (SLC26Dg) of the solute carrier SLC26 family of anion transporters has allowed us to create 3-dimensional models of all 10 human members (SLC26A1-A11, A10 being a pseudogene) of these membrane proteins using the Phyre2 bioinformatic tool. The homology modeling predicted that the SLC26 human proteins, like the SLC26Dg template, all consist of 14 transmembrane segments (TM) arranged in a 7+7 inverted topology with the amino-termini of two half-helices (TM3 and 10) facing each other in the centre of the protein to create the anion-binding site, linked to a C-terminal cytosolic sulfate transporter anti-sigma factor antagonist (STAS) domain. A plethora of human diseases are associated with mutations in the genes encoding human SLC26 transporters, including chondrodysplasias with varying severity in SLC26A2 (50 mutations, 27 point mutations), congenital chloride-losing diarrhea in SLC26A3 (70 mutations, 31 point mutations) and Pendred Syndrome or deafness autosomal recessive type 4 in SLC26A4 (~500 mutations, 203 point mutations). We have localized all of these point mutations in the 3-dimensional structures of the respective SLC26A2, A3 and A4 proteins and systematically analyzed their effect on protein structure. While most disease-causing mutations may cause folding defects resulting in impaired trafficking of these membrane glycoproteins from the endoplasmic reticulum to the cell surface - as demonstrated in a number of functional expression studies - the modeling also revealed that a number of pathogenic mutations are localized to the anion-binding site, which may directly affect transport function.
第一个阴离子转运体溶质载体家族 SLC26 成员(SLC26Dg)的晶体结构的出现,使得我们能够使用 Phyre2 生物信息学工具创建所有 10 个人类成员(SLC26A1-A11,A10 是假基因)的 3 维模型。同源建模预测,SLC26 人类蛋白与 SLC26Dg 模板一样,都由 14 个跨膜段(TM)组成,以 7+7 反向拓扑排列,两个半环(TM3 和 10)的氨基末端相对,在蛋白质中心形成阴离子结合位点,并与 C 末端胞质硫酸盐转运反西格玛因子拮抗剂(STAS)结构域相连。大量人类疾病与编码人类 SLC26 转运蛋白的基因突变有关,包括 SLC26A2 中不同严重程度的软骨发育不良(50 个突变,27 个点突变)、SLC26A3 中的先天性氯丢失性腹泻(70 个突变,31 个点突变)和 Pendred 综合征或常染色体隐性遗传 4 型耳聋 SLC26A4(~500 个突变,203 个点突变)。我们已经将所有这些点突变定位在各自的 SLC26A2、A3 和 A4 蛋白的 3 维结构中,并系统地分析了它们对蛋白质结构的影响。虽然大多数致病突变可能导致折叠缺陷,从而使这些膜糖蛋白从内质网向细胞表面的运输受损——正如许多功能表达研究所示——建模还表明,一些致病性突变定位于阴离子结合位点,这可能直接影响转运功能。