細(xì)菌為了保持它們的形狀可是沒少下工夫，然而盡管科學(xué)家已經(jīng)知道幾種蛋白質(zhì)在桿狀菌保持形狀的過程中功不可沒，但決定細(xì)胞形狀的機(jī)制依然是個(gè)未解之謎,。如今,，在日前出版的《EMBO雜志》上,，日本科學(xué)家描述了一種蛋白質(zhì),，它能夠調(diào)整細(xì)胞的長(zhǎng)度,，但無(wú)法調(diào)節(jié)寬度,。
日本國(guó)立遺傳學(xué)研究所的Daisuke Shiomi，Masako Sakai和Hironori Niki通過對(duì)單獨(dú)的變異大腸桿菌菌株在顯微鏡下進(jìn)行觀察,，鑒別出了一些圓形或橢圓形細(xì)胞,，這些細(xì)胞的一種基因產(chǎn)生了突變,，研究人員將其重新命名為rodZ,。rodZ突變的細(xì)胞具有生存能力,，但生長(zhǎng)得非常緩慢，同時(shí)精細(xì)定量研究顯示,，雖然rodZ細(xì)胞長(zhǎng)得要比野生型細(xì)菌短一些,，但它們通常會(huì)更寬一些,。與此形成對(duì)照的是,，當(dāng)MreB或Pbp2——之前發(fā)現(xiàn)的兩種與細(xì)胞形狀有關(guān)的蛋白質(zhì)——被抑制后,，細(xì)胞會(huì)變得更寬,，但卻保持了它們的長(zhǎng)度,。
研究人員發(fā)現(xiàn),，由此編碼產(chǎn)生的RodZ是一種整合內(nèi)膜蛋白質(zhì),，可以在細(xì)胞周圍形成螺旋，并且能夠與MreB聯(lián)合定位,。但是,，MreB和RodZ彼此正確的定位卻不需要對(duì)方。通過RodZ,，蛋白質(zhì)中細(xì)胞質(zhì)部分的一個(gè)螺旋—轉(zhuǎn)折—螺旋區(qū)域是螺旋的形成所必需的,，而橫跨膜的區(qū)域以及周質(zhì)區(qū)域卻是維持細(xì)胞形狀所必需的。有趣的是,，一樣分散在質(zhì)膜中的RodZ的刪節(jié)形式卻能夠部分補(bǔ)充rodZ的刪除,，意味著保持其功能并不是這種蛋白質(zhì)的定位所必須的。RodZ的同類物廣泛分布在桿狀的γ-變形菌綱中,。
研究人員提出了細(xì)胞維持形狀的一種模式,，即細(xì)胞的長(zhǎng)度和寬度分別是獨(dú)自調(diào)節(jié)的：MreB和Pbp2保持細(xì)胞的寬度，而RodZ則調(diào)節(jié)長(zhǎng)度,。針對(duì)這一模型的更多證據(jù)來自于RodZ的過度表達(dá),，它導(dǎo)致了細(xì)胞長(zhǎng)度的少量增加。研究人員下一步需要搞清RodZ的功能是如何保持細(xì)胞形狀的,。（生物谷Bioon.com）
生物谷推薦原始出處：
The EMBO Journal (2008) 27, 3081–3091, doi:10.1038/emboj.2008.234
Determination of bacterial rod shape by a novel cytoskeletal membrane protein
Daisuke Shiomi1, Masako Sakai1 and Hironori Niki1, 2
1 Microbial Genetics Laboratory, Genetic Strains Research Center, National Institute of Genetics, Mishima, Japan
2 Department of Genetics, The Graduate University for Advanced Studies, Mishima (SOKENDAI), Shizuoka, Japan
Cell shape is critical for growth, and some genes are involved in bacterial cell morphogenesis. Here, we report a novel gene, rodZ, required for the determination of rod shape in Escherichia coli. Cells lacking rodZ no longer had rod shape but rather were round or oval. These round cells were smaller than known round mutant cells, including mreB and pbpA mutants; both are known to lose rod shape. Morphogenesis from rod cells to round cells and vice versa, caused by depletion and overproduction of RodZ, respectively, revealed that RodZ could regulate the length of the long axis of the cell. RodZ is a membrane protein with bitopic topology such that the N-terminal region including a helix-turn-helix motif is in the cytoplasm, whereas the C-terminal region is exposed in the periplasm. GFP–RodZ forms spirals along the lateral axis of the cell beneath the cell membrane, similar to the MreB bacterial actin. Thus, RodZ may mediate spatial information from cytoskeletal proteins in the cytoplasm to a peptidoglycan synthesis machinery in the periplasm.
