Nodelman I M, Bowman G D, Lindberg U, Schutt C E
Department of Molecular Biology, Henry H. Hoyt Laboratory, Princeton University, Princeton, NJ 08544, USA.
J Mol Biol. 1999 Dec 17;294(5):1271-85. doi: 10.1006/jmbi.1999.3318.
Human profilins are multifunctional, single-domain proteins which directly link the actin microfilament system to a variety of signalling pathways via two spatially distinct binding sites. Profilin binds to monomeric actin in a 1:1 complex, catalyzes the exchange of the actin-bound nucleotide and regulates actin filament barbed end assembly. Like SH3 domains, profilin has a surface-exposed aromatic patch which binds to proline-rich peptides. Various multidomain proteins including members of the Ena/VASP and formin families localize profilin:actin complexes through profilin:poly-L-proline interactions to particular cytoskeletal locations (e.g. focal adhesions, cleavage furrows). Humans express a basic (I) and an acidic (II) isoform of profilin which exhibit different affinities for peptides and proteins rich in proline residues. Here, we report the crystallization and X-ray structure determination of human profilin II to 2.2 A. This structure reveals an aromatic extension of the previously defined poly-L-proline binding site for profilin I. In contrast to serine 29 of profilin I, tyrosine 29 in profilin II is capable of forming an additional stacking interaction and a hydrogen bond with poly-L-proline which may account for the increased affinity of the second isoform for proline-rich peptides. Differential isoform specificity for proline-rich proteins may be attributed to the differences in charged and hydrophobic residues in and proximal to the poly-L-proline binding site. The actin-binding face remains nearly identical with the exception of five amino acid differences. These observations are important for the understanding of the functional and structural differences between these two classes of profilin isoforms.
人源肌动蛋白单体结合蛋白是多功能的单结构域蛋白，通过两个空间上不同的结合位点将肌动蛋白微丝系统直接与多种信号通路相连。肌动蛋白单体结合蛋白以1:1复合物的形式与单体肌动蛋白结合，催化肌动蛋白结合核苷酸的交换，并调节肌动蛋白丝的带刺末端组装。与SH3结构域一样，肌动蛋白单体结合蛋白有一个暴露于表面的芳香族斑块，可与富含脯氨酸的肽结合。包括Ena/VASP和formin家族成员在内的各种多结构域蛋白通过肌动蛋白单体结合蛋白：聚-L-脯氨酸相互作用将肌动蛋白单体结合蛋白：肌动蛋白复合物定位到特定的细胞骨架位置（如粘着斑、分裂沟）。人类表达肌动蛋白单体结合蛋白的一种碱性（I）异构体和一种酸性（II）异构体，它们对富含脯氨酸残基的肽和蛋白质表现出不同的亲和力。在此，我们报告了人源肌动蛋白单体结合蛋白II的结晶及X射线晶体结构测定，分辨率达到2.2 Å。该结构揭示了先前定义的肌动蛋白单体结合蛋白I的聚-L-脯氨酸结合位点的芳香族延伸。与肌动蛋白单体结合蛋白I的丝氨酸29不同，肌动蛋白单体结合蛋白II中的酪氨酸29能够与聚-L-脯氨酸形成额外的堆积相互作用和氢键，这可能解释了第二种异构体对富含脯氨酸肽的亲和力增加的原因。对富含脯氨酸蛋白质的异构体特异性差异可能归因于聚-L-脯氨酸结合位点及其附近带电和疏水残基的差异。除了五个氨基酸差异外，肌动蛋白结合面几乎保持相同。这些观察结果对于理解这两类肌动蛋白单体结合蛋白异构体之间的功能和结构差异很重要。
