Broeker Nina K, Barbirz Stefanie
Physikalische Biochemie, Universita¨t Potsdam, Karl-Liebknecht-Str. 24-25, Potsdam 14476, Germany.
Mol Microbiol. 2017 Aug;105(3):353-357. doi: 10.1111/mmi.13729. Epub 2017 Jul 6.
Tailed bacteriophages specific for Gram-negative bacteria encounter lipopolysaccharide (LPS) during the first infection steps. Yet, it is not well understood how biochemistry of these initial interactions relates to subsequent events that orchestrate phage adsorption and tail rearrangements to initiate cell entry. For many phages, long O-antigen chains found on the LPS of smooth bacterial strains serve as essential receptor recognized by their tailspike proteins (TSP). Many TSP are depolymerases and O-antigen cleavage was described as necessary step for subsequent orientation towards a secondary receptor. However, O-antigen specific host attachment must not always come along with O-antigen degradation. In this issue of Molecular Microbiology Prokhorov et al. report that coliphage G7C carries a TSP that deacetylates O-antigen but does not degrade it, whereas rough strains or strains lacking O-antigen acetylation remain unaffected. Bacteriophage G7C specifically functionalizes its tail by attaching the deacetylase TSP directly to a second TSP that is nonfunctional on the host's O-antigen. This challenges the view that bacteriophages use their TSP only to clear their way to a secondary receptor. Rather, O-antigen specific phages may employ enzymatically active TSP as a tool for irreversible LPS membrane binding to initiate subsequent infection steps.
特异性针对革兰氏阴性菌的有尾噬菌体在初次感染步骤中会遇到脂多糖（LPS）。然而，这些初始相互作用的生物化学过程如何与随后协调噬菌体吸附和尾部重排以启动细胞进入的事件相关联，目前还不太清楚。对于许多噬菌体而言，光滑细菌菌株LPS上发现的长O抗原链是其尾刺蛋白（TSP）识别的必需受体。许多TSP是解聚酶，O抗原裂解被描述为随后定向至二级受体的必要步骤。然而，O抗原特异性宿主附着并不总是伴随着O抗原降解。在本期《分子微生物学》中，普罗霍罗夫等人报道，大肠杆菌噬菌体G7C携带一种能使O抗原脱乙酰化但不降解它的TSP，而粗糙菌株或缺乏O抗原乙酰化的菌株则不受影响。噬菌体G7C通过将脱乙酰酶TSP直接连接到在宿主O抗原上无功能的第二个TSP上，使其尾部具有特定功能。这对噬菌体仅利用其TSP来清除通往二级受体的途径这一观点提出了挑战。相反，O抗原特异性噬菌体可能利用具有酶活性的TSP作为不可逆结合LPS膜以启动后续感染步骤的工具。
