Chim Nicholas, Gall Walter E, Xiao Jing, Harris Mark P, Graham Todd R, Krezel Andrzej M
Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37232, USA.
Proteins. 2004 Mar 1;54(4):784-93. doi: 10.1002/prot.10636.
The SWA2/AUX1 gene has been proposed to encode the Saccharomyces cerevisiae ortholog of mammalian auxilin. Swa2p is required for clathrin assembly/dissassembly in vivo, thereby implicating it in intracellular protein and lipid trafficking. While investigating the 287-residue N-terminal region of Swa2p, we found a single stably folded domain between residues 140 and 180. Using binding assays and structural analysis, we established this to be a ubiquitin-associated (UBA) domain, unidentified by bioinformatics of the yeast genome. We determined the solution structure of this Swa2p domain and found a characteristic three-helix UBA fold. Comparisons of structures of known UBA folds reveal that the position of the third helix is quite variable. This helix in Swa2p UBA contains a bulkier tyrosine in place of smaller residues found in other UBAs and cannot pack as close to the second helix. The molecular surface of Swa2p UBA has a mostly negative potential, with a single hydrophobic surface patch found also in the UBA domains of human protein, HHR23A. The presence of a UBA domain implicates Swa2p in novel roles involving ubiquitin and ubiquitinated substrates. We propose that Swa2p is a multifunctional protein capable of recognizing several proteins through its protein-protein recognition domains.
SWA2/AUX1基因被认为编码了与哺乳动物辅助蛋白同源的酿酒酵母蛋白。Swa2p在体内网格蛋白的组装/拆卸过程中是必需的，因此参与细胞内蛋白质和脂质的运输。在研究Swa2p的287个氨基酸的N端区域时，我们在第140至180位氨基酸之间发现了一个单一的稳定折叠结构域。通过结合试验和结构分析，我们确定这是一个泛素相关（UBA）结构域，在酵母基因组的生物信息学分析中未被识别。我们测定了该Swa2p结构域的溶液结构，发现了一个典型的三螺旋UBA折叠。已知UBA折叠结构的比较表明，第三个螺旋的位置变化很大。Swa2p UBA中的这个螺旋含有一个较大的酪氨酸，取代了其他UBA中发现的较小残基，并且不能像其他UBA那样紧密地与第二个螺旋堆积。Swa2p UBA的分子表面大部分带负电，在人类蛋白HHR23A的UBA结构域中也发现了一个单一的疏水表面区域。UBA结构域的存在表明Swa2p参与了涉及泛素和泛素化底物的新功能。我们提出Swa2p是一种多功能蛋白，能够通过其蛋白质-蛋白质识别结构域识别多种蛋白质。
