den Engelsman John, Keijsers Vivian, de Jong Wilfried W, Boelens Wilbert C
Department of Biochemistry, Nÿmegen Center for Molecular Life Sciences, University of Nijmegen, 6500 HB Nijmegen, The Netherlands.
J Biol Chem. 2003 Feb 14;278(7):4699-704. doi: 10.1074/jbc.M211403200. Epub 2002 Dec 4.
AlphaB-crystallin is a small heat-shock protein in which three serine residues (positions 19, 45, and 59) can be phosphorylated under various conditions. We describe here the interaction of alphaB-crystallin with FBX4, an F-box-containing protein that is a component of the ubiquitin-protein isopeptide ligase SCF (SKP1/CUL1/F-box). The interaction with FBX4 was enhanced by mimicking phosphorylation of alphaB-crystallin at both Ser-19 and Ser-45 (S19D/S45D), but not at other combinations. Ser-19 and Ser-45 are preferentially phosphorylated during the mitotic phase of the cell cycle. Also alphaB-crystallin R120G, a mutant found to co-segregate with a desmin-related myopathy, displayed increased interaction with FBX4. Both alphaB-crystallin S19D/S45D and R120G specifically translocated FBX4 to the detergent-insoluble fraction and stimulated the ubiquitination of one or a few yet unknown proteins. These findings implicate the involvement of alphaB-crystallin in the ubiquitin/proteasome pathway in a phosphorylation- and cell cycle-dependent manner and may provide new insights into the alphaB-crystallin-induced aggregation in desmin-related myopathy.
αB-晶状体蛋白是一种小分子热休克蛋白，其中三个丝氨酸残基（第19、45和59位）在各种条件下均可被磷酸化。我们在此描述αB-晶状体蛋白与FBX4的相互作用，FBX4是一种含F-盒的蛋白，是泛素-蛋白异肽连接酶SCF（SKP1/CUL1/F-盒）的一个组分。通过模拟αB-晶状体蛋白在Ser-19和Ser-45处的磷酸化（S19D/S45D），而非其他组合，可增强与FBX4的相互作用。Ser-19和Ser-45在细胞周期的有丝分裂期优先被磷酸化。此外，αB-晶状体蛋白R120G（一种被发现与结蛋白相关肌病共分离的突变体）与FBX4的相互作用增强。αB-晶状体蛋白S19D/S45D和R120G均特异性地将FBX4转运至去污剂不溶性组分，并刺激一种或几种未知蛋白的泛素化。这些发现表明αB-晶状体蛋白以磷酸化和细胞周期依赖性方式参与泛素/蛋白酶体途径，并可能为αB-晶状体蛋白在结蛋白相关肌病中诱导的聚集提供新的见解。
