Fransen Marc, Amery Leen, Hartig Andreas, Brees Chantal, Rabijns Anja, Mannaerts Guy P, Van Veldhoven Paul P
Katholieke Universiteit Leuven, Campus Gasthuisberg (O&N 1), Departement Moleculaire Celbiologie, LIPIT, Leuven, Belgium.
Biochim Biophys Acta. 2008 May;1783(5):864-73. doi: 10.1016/j.bbamcr.2008.02.013. Epub 2008 Feb 29.
Tetratricopeptide (TPR)-domain proteins are involved in various cellular processes. The TPR domain is known to be responsible for interaction with other proteins commonly recognizing sequence motifs at the C-termini. One such TPR-protein, TRIP8b, was originally identified in rat as an interaction partner of Rab8b, and its human orthologue as a protein related to the peroxisomal targeting signal 1 (PTS1) receptor Pex5p (Pex5Rp). Somewhat later, the mouse orthologue was reported to bind the hyperpolarization-activated, cyclic nucleotide-regulated HCN channels, and, very recently, the rat orthologue was shown to interact with latrophilin 1, the calcium-independent receptor of alpha-latrotoxin. Here we employed various methodological approaches to investigate and compare the binding specificities of the human PTS1 receptor Pex5p and the related protein Pex5Rp/TRIP8b towards a subset of targets, including Rab8b and various C-termini resembling PTS1. The results show that the TPR domains of Pex5p and Pex5Rp/TRIP8b have distinct but overlapping substrate specificities. This suggests that selectivity in the recognition of substrates by the TPR domains of Pex5p and Pex5Rp/TRIP8b is a matter of considerable complexity, and that no single determinant appears to be sufficient in unambiguously defining a binding target for either protein. This idea is further corroborated by our observations that changes in the surrounding residues or the conformational state of one of the binding partners can profoundly alter their binding activities. The implications of these findings for the possible peroxisome-related functions of Pex5Rp/TRIP8b are discussed.
四肽重复序列（TPR）结构域蛋白参与多种细胞过程。已知TPR结构域负责与其他通常识别C末端序列基序的蛋白质相互作用。一种这样的TPR蛋白，TRIP8b，最初在大鼠中被鉴定为Rab8b的相互作用伙伴，其人类同源物是一种与过氧化物酶体靶向信号1（PTS1）受体Pex5p（Pex5Rp）相关的蛋白质。稍后，据报道小鼠同源物可结合超极化激活的环核苷酸调节HCN通道，并且最近，大鼠同源物被证明可与latrophilin 1相互作用，latrophilin 1是α-蝰蛇毒素的钙非依赖性受体。在这里，我们采用了各种方法来研究和比较人类PTS1受体Pex5p和相关蛋白Pex5Rp/TRIP8b对包括Rab8b和各种类似PTS1的C末端在内的一组靶标的结合特异性。结果表明，Pex5p和Pex5Rp/TRIP8b的TPR结构域具有不同但重叠的底物特异性。这表明Pex5p和Pex5Rp/TRIP8b的TPR结构域在识别底物时的选择性是一个相当复杂的问题，并且似乎没有单一的决定因素足以明确地定义这两种蛋白质的结合靶标。我们的观察结果进一步证实了这一观点，即结合伙伴之一周围残基的变化或构象状态的改变可深刻改变它们的结合活性。讨论了这些发现对Pex5Rp/TRIP8b可能的过氧化物酶体相关功能的影响。
