Erales Jenny, Lignon Sabrina, Gontero Brigitte
Laboratoire d'Enzymologie de Complexes Supramoléculaires, UPR 9036, Bioénergétique et Ingénierie des Protéines, Marseille Cedex 20, France.
J Biol Chem. 2009 May 8;284(19):12735-44. doi: 10.1074/jbc.M808254200. Epub 2009 Mar 14.
A new role is reported for CP12, a highly unfolded and flexible protein, mainly known for its redox function with A(4) glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Both reduced and oxidized CP12 can prevent the in vitro thermal inactivation and aggregation of GAPDH from Chlamydomonas reinhardtii. This mechanism is thus not redox-dependent. The protection is specific to CP12, because other proteins, such as bovine serum albumin, thioredoxin, and a general chaperone, Hsp33, do not fully prevent denaturation of GAPDH. Furthermore, CP12 acts as a specific chaperone, since it does not protect other proteins, such as catalase, alcohol dehydrogenase, or lysozyme. The interaction between CP12 and GAPDH is necessary to prevent the aggregation and inactivation, since the mutant C66S that does not form any complex with GAPDH cannot accomplish this protection. Unlike the C66S mutant, the C23S mutant that lacks the N-terminal bridge is partially able to protect and to slow down the inactivation and aggregation. Tryptic digestion coupled to mass spectrometry confirmed that the S-loop of GAPDH is the interaction site with CP12. Thus, CP12 not only has a redox function but also behaves as a specific "chaperone-like protein" for GAPDH, although a stable and not transitory interaction is observed. This new function of CP12 may explain why it is also present in complexes involving A(2)B(2) GAPDHs that possess a regulatory C-terminal extension (GapB subunit) and therefore do not require CP12 to be redox-regulated.
据报道，CP12具有一种新功能，它是一种高度展开且灵活的蛋白质，主要因其与A(4)甘油醛-3-磷酸脱氢酶（GAPDH）的氧化还原功能而为人所知。还原态和氧化态的CP12都能防止莱茵衣藻的GAPDH在体外发生热失活和聚集。因此，这种机制不依赖于氧化还原。这种保护作用对CP12具有特异性，因为其他蛋白质，如牛血清白蛋白、硫氧还蛋白和通用伴侣蛋白Hsp33，不能完全防止GAPDH变性。此外，CP12作为一种特异性伴侣蛋白，因为它不能保护其他蛋白质，如过氧化氢酶、乙醇脱氢酶或溶菌酶。CP12与GAPDH之间的相互作用对于防止聚集和失活是必要的，因为不与GAPDH形成任何复合物的C66S突变体无法实现这种保护。与C66S突变体不同，缺乏N端桥的C23S突变体能够部分保护并减缓失活和聚集。胰蛋白酶消化结合质谱分析证实，GAPDH的S环是与CP12的相互作用位点。因此，CP12不仅具有氧化还原功能，而且对于GAPDH还表现为一种特异性的“类伴侣蛋白”，尽管观察到的是一种稳定而非短暂的相互作用。CP12的这种新功能可能解释了为什么它也存在于涉及A(2)B(2) GAPDHs的复合物中，这些GAPDHs具有一个调节性的C端延伸（GapB亚基），因此不需要CP12进行氧化还原调节。
