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首页> 外文期刊>Journal of Molecular Biology >MODEL STRUCTURE OF THE OMP-ALPHA ROD, A PARALLEL FOUR-STRANDED COILED COIL FROM THE HYPERTHERMOPHILIC EUBACTERIUM THERMOTOGA MARITIMA
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MODEL STRUCTURE OF THE OMP-ALPHA ROD, A PARALLEL FOUR-STRANDED COILED COIL FROM THE HYPERTHERMOPHILIC EUBACTERIUM THERMOTOGA MARITIMA

机译：超嗜热EU鱼海藻的平行四层螺旋卷材OMP-Alpha杆的模型结构

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Ompa is an outer-membrane protein that spans the periplasmic space of the hyperthermophilic eubacterium Thermotoga maritima. The molecule contains a globular head with an apparent diameter of 8 nm and a rod-shaped tail of 40 nm length. The sequence of the globular domain is homologous to a conserved region of cell wall-bound proteins and probably attaches Ompa to the peptidoglycan. The sequence of the rod domain resembles that of coiled coil proteins and ends in a transmembrane segment that anchors Omp alpha to the outer membrane. We have analysed Ompa by scanning transmission electron microscopy (STEM) and by statistical sequence analysis methods. The Ompa rod is a tetramer with an unusual periodicity of hydrophobic residues close to 3.6 that differs from the 3.5 periodicity of canonical coiled coils. This is due to periodic omissions of three residues in the heptad repeat pattern (''stutters'') whose effect is to locally distort the packing of hydrophobic layers in the core of the coiled coil. Residues in position a are shifted to occupy a position halfway between positions a and d (x layers) and residues in positions d and e are shifted so that both participate in core packing interactions (da layers). Such distorted layers are frequently found in helical bundles and are characteristic of helices that do not undergo supercoiling. The only homo-oligomeric coiled coil of known structure which contains x and da layers is the three-stranded coiled coil of influenza haemagglutinin. Using geometric constraints derived from this structure, we have built a model for the Ompa rod in which the helices have a crossing angle of less than 15 degrees and maintain a residual degree of supercoiling with a pitch of approximately 40 nm. Our analysis of distorted layers in the hydrophobic core of coiled coils and helical bundles shows that stutters must not be viewed as discontinuities but rather as a departure from the canonical ''knobs-into-holes'' packing that allows helices to interact at a low angle without supercoiling. Although stutters have been considered to weaken helical interactions, their occurrence in a rigid, highly thermostable coiled coil indicates that this may not be generally true. Our analysis also indicates that skips and stutters are two different conventions for describing the same underlying structural feature. [References: 35]
机译：Ompa是一种跨膜蛋白，横跨超嗜热真细菌马氏嗜热菌的周质空间。该分子包含一个表观直径为8 nm的球形头部和一个40 nm长的杆状尾巴。球状结构域的序列与细胞壁结合蛋白的保守区域同源，并且可能使Ompa与肽聚糖连接。杆结构域的序列类似于卷曲螺旋蛋白的序列，并终止于跨膜片段，该片段将Ompα锚定在外膜上。我们已经通过扫描透射电子显微镜（STEM）和统计序列分析方法对Ompa进行了分析。 Ompa棒是四聚体，其疏水性残基的异常周期接近3.6，与规范性线圈的3.5周期不同。这是由于七肽重复模式（“口吃”）中三个残基的周期性遗漏所致，其作用是局部扭曲盘绕线圈芯中疏水层的堆积。位置a的残基移位以占据位置a和d之间的中间位置（x层），位置d和e的残基移位，以使它们都参与芯堆积相互作用（da层）。这种扭曲的层通常在螺旋束中发现，并且是未经历超螺旋的螺旋的特征。含有x和da层的已知结构的唯一同低聚卷曲螺旋是流感血凝素的三链卷曲螺旋。使用从该结构派生的几何约束，我们为Ompa杆建立了一个模型，其中螺旋的交叉角小于15度，并以大约40 nm的间距保持剩余的超螺旋度。我们对盘绕的线圈和螺旋束的疏水芯中变形层的分析表明，口吃不应该被视为不连续，而应视为偏离规范的“旋钮-入孔”填充，后者允许螺旋在低位相互作用角度无超卷。尽管已经认为口吃会削弱螺旋相互作用，但它们在刚性，高度热稳定的盘绕线圈中的出现表明，通常情况可能并非如此。我们的分析还表明，跳过和断断续续是描述相同底层结构特征的两种不同约定。 [参考：35]

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