Haddad Alex, Rose R Wesley, Pohlschröder Mechthild
Department of Biology, University of Pennsylvania, Philadelphia 19104, USA.
J Bacteriol. 2005 Jun;187(12):4015-22. doi: 10.1128/JB.187.12.4015-4022.2005.
The targeting of many Sec substrates to the membrane-associated translocation pore requires the cytoplasmic signal recognition particle (SRP). In Eukarya and Bacteria it has been shown that membrane docking of the SRP-substrate complex occurs via the universally conserved SRP receptor (Sralpha/beta and FtsY, respectively). While much has been learned about the archaeal SRP in recent years, few studies have examined archaeal Sralpha/FtsY homologs. In the present study the FtsY homolog of Haloferax volcanii was characterized in its native host. Disruption of the sole chromosomal copy of ftsY in H. volcanii was possible only under conditions where either the full-length haloarchaeal FtsY or an amino-terminally truncated version of this protein lacking the A domain, was expressed in trans. Subcellular fractionation analysis of H. volcanii ftsY deletion strains expressing either one of the complementing proteins revealed that in addition to a cytoplasmic pool, both proteins cofractionate with the haloarchaeal cytoplasmic membrane. Moreover, membrane localization of the universally conserved SRP subunit SRP54, the key binding partner of FtsY, was detected in both H. volcanii strains. These analyses suggest that the H. volcanii FtsY homolog plays a crucial role but does not require its A domain for haloarchaeal growth.
许多信号肽酶底物靶向与膜相关的转运孔需要细胞质信号识别颗粒（SRP）。在真核生物和细菌中，已表明SRP-底物复合物的膜对接是通过普遍保守的SRP受体（分别为Sralpha/beta和FtsY）发生的。尽管近年来对古菌SRP已有很多了解，但很少有研究考察古菌Sralpha/FtsY同源物。在本研究中，对嗜盐嗜碱菌（Haloferax volcanii）的FtsY同源物在其天然宿主中进行了表征。仅在全长嗜盐古菌FtsY或该蛋白缺乏A结构域的氨基末端截短版本在反式中表达的条件下，才可能破坏嗜盐嗜碱菌中ftsY的唯一染色体拷贝。对表达任一互补蛋白的嗜盐嗜碱菌ftsY缺失菌株进行亚细胞分级分离分析表明，除了细胞质池外，这两种蛋白都与嗜盐古菌细胞质膜共分级。此外，在两种嗜盐嗜碱菌菌株中均检测到FtsY的关键结合伴侣——普遍保守的SRP亚基SRP54的膜定位。这些分析表明，嗜盐嗜碱菌FtsY同源物起着关键作用，但嗜盐古菌生长不需要其A结构域。
