Institute of Biology/Microbiology, University of Halle-Wittenberg, Kurt-Mothes-Str. 3, D-06120 Halle, Germany.
FEBS Lett. 2010 Aug 20;584(16):3644-8. doi: 10.1016/j.febslet.2010.07.039. Epub 2010 Jul 24.
The twin-arginine translocation (Tat) system translocates folded proteins across biological membranes. It has been suggested that the Tat system of Escherichia coli can direct Tat substrates to degradation if they are not properly folded [Matos, C.F., Robinson, C. and Di Cola, A. (2008) The Tat system proofreads FeS protein substrates and directly initiates the disposal of rejected molecules. EMBO J. 27, 2055-2063; Matos, C.F., Di Cola, A. and Robinson, C. (2009) TatD is a central component of a Tat translocon-initiated quality control system for exported FeS proteins in Escherichia coli. EMBO Rep. 10, 474-479]. Contrary to the earlier reports, it is now concluded that reported differences between tested strains were due to variations in expression levels and inclusion body formation. Using the native Tat substrate NrfC and a malfolded variant thereof, we show that the turnover of these proteins is not affected by the absence of all known Tat components. Malfolded NrfC is degraded more quickly than the native protein, indicating that Tat-independent protease systems can recognize malfolded Tat substrates.
双精氨酸转运（Tat）系统将折叠蛋白跨生物膜转运。有人提出，如果大肠杆菌的 Tat 系统不能正确折叠 Tat 底物，它可以将其导向降解[Matos, C.F., Robinson, C. 和 Di Cola, A. (2008) Tat 系统校对 FeS 蛋白底物，并直接启动对不合格分子的处理。EMBO J. 27, 2055-2063; Matos, C.F., Di Cola, A. 和 Robinson, C. (2009) TatD 是大肠杆菌中 Tat 易位起始的 FeS 蛋白出口质量控制系统的核心组成部分。EMBO Rep. 10, 474-479]。与早期的报道相反，现在的结论是，测试菌株之间的差异是由于表达水平和包涵体形成的差异。使用天然 Tat 底物 NrfC 和其错误折叠的变体，我们表明这些蛋白质的周转不受所有已知 Tat 成分缺失的影响。错误折叠的 NrfC 比天然蛋白降解得更快，这表明 Tat 非依赖性蛋白酶系统可以识别错误折叠的 Tat 底物。
