Lalor T M, Kjeldgaard M, Shimamoto G T, Strickler J E, Konigsberg W H, Richards F F
Proc Natl Acad Sci U S A. 1984 Feb;81(4):998-1002. doi: 10.1073/pnas.81.4.998.
Infection with the African trypanosomes gives rise to relapsing waves of parasitemia in the host. A predominant population of trypanosomes is present in each wave, and such predominant populations are usually serologically distinct from each other. Trypanosomes are covered by an extramembranous, highly antigenic, variant-specific glycoprotein coat that is 15 nm thick. The primary structure of a large portion of the glycoprotein molecule is different in the predominant trypanosome populations of each parasitemic wave. Analysis of the secondary structure potential of five full-length and five partial amino acid sequences of variant-specific glycoproteins from members of the Trypanosoma brucei complex has been carried out. The potentials for alpha-helix, beta-turns, and beta-strand structure have been calculated. A high degree of alpha-helical structure potential is present in all the full-length or partial sequences examined. There is conservation of secondary structure potential in the COOH-terminal 100 amino acids, where both partial and complete conservation of primary amino acid sequence exists. The NH2-terminal regions are rich in alpha-helix potential. However, over large stretches of the middle of the VSG molecules there is wide diversity of secondary structure potential. This suggests that tertiary folding structures may also be different in this region. If these predictions are true, different regions of the variant-specific glycoprotein could be exposed to the solvent in different variant-specific trypanosome serotypes. The implication is that antigenic variation is mediated by a polygene family of glycoproteins containing highly polymorphic regions. These could fold differently and expose different surface regions of the protein to the solvent. This device might reduce immune crossreactivity among members of the variant-specific glycoprotein family.
感染非洲锥虫会在宿主体内引发寄生虫血症的复发浪潮。每一波中都存在占主导地位的锥虫群体，而且这些占主导地位的群体通常在血清学上彼此不同。锥虫被一层15纳米厚的膜外、高度抗原性、变体特异性糖蛋白外壳所覆盖。在每一波寄生虫血症的占主导地位的锥虫群体中，糖蛋白分子大部分的一级结构是不同的。已经对布氏锥虫复合体成员的变体特异性糖蛋白的五个全长和五个部分氨基酸序列的二级结构潜力进行了分析。计算了α螺旋、β转角和β链结构的潜力。在所检测的所有全长或部分序列中都存在高度的α螺旋结构潜力。在COOH末端的100个氨基酸中存在二级结构潜力的保守性，其中存在一级氨基酸序列的部分和完全保守。NH2末端区域富含α螺旋潜力。然而，在VSG分子中间的大片区域，二级结构潜力存在广泛差异。这表明该区域的三级折叠结构也可能不同。如果这些预测是正确的，那么在不同变体特异性锥虫血清型中，变体特异性糖蛋白的不同区域可能会暴露于溶剂中。这意味着抗原变异是由包含高度多态性区域的糖蛋白多基因家族介导的。这些糖蛋白可能会以不同方式折叠，并将蛋白质的不同表面区域暴露于溶剂中。这种机制可能会降低变体特异性糖蛋白家族成员之间的免疫交叉反应性。
