Walker Richard L, Runyan Catherine A
California Animal Health and Food Safety Laboratory School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Am J Vet Res. 2003 Aug;64(8):976-81. doi: 10.2460/ajvr.2003.64.976.
To determine whether previously unidentified variations of the SzP protein of Streptococcus equi subsp zooepidemicus were present in horses with various clinical signs of infection and whether any relationship could be identified between SzP protein variants and naturally occurring clinical conditions.
23 isolates of S equi subsp zooepidemicus were recovered from specimens of horses with various clinical conditions and used as a representative population of isolates for evaluation of different SzP protein variants.
Genetic heterogeneity of the isolates was demonstrated by repetitive extragenic palindromic-polymerase chain reaction analysis. The SzP gene was sequenced and the presumed protein sequence determined for each isolate. Characteristics of the SzP proteins were compared among the isolates and in relation to the clinical conditions of horses from which they were recovered.
The signal peptide types, number of proline-glutamic acid-proline-lysine repeats, and anchor sequences were consistent with those previously described for the SzP protein. Many of the isolates clustered with 5 previously described types on the basis of the hypervariable region of the SzP protein. One additional variant, which represented 8 of the isolates, was identified. Particular motifs in the hypervariable region accounted for many of the differences among hypervariable types.
The SzP protein appears to be limited to a selected number of types. Variations in the SzP protein are frequently determined on the basis of different motifs rather than random amino acid substitutions. There does not appear to be any association of SzP protein variations and clinical manifestations of infection in horses.
确定马链球菌兽疫亚种（Streptococcus equi subsp zooepidemicus）的SzP蛋白中先前未被识别的变异是否存在于具有各种感染临床症状的马匹中，以及是否能确定SzP蛋白变体与自然发生的临床病症之间存在任何关联。
从患有各种临床病症的马匹标本中分离出23株马链球菌兽疫亚种，用作评估不同SzP蛋白变体的代表性分离株群体。
通过重复外显子回文 - 聚合酶链反应分析证明分离株的遗传异质性。对SzP基因进行测序，并确定每个分离株的推测蛋白序列。比较分离株之间的SzP蛋白特征，并与分离出这些菌株的马匹的临床病症相关联。
信号肽类型、脯氨酸 - 谷氨酸 - 脯氨酸 - 赖氨酸重复序列的数量和锚定序列与先前描述的SzP蛋白一致。根据SzP蛋白的高变区，许多分离株与先前描述的5种类型聚类。另外鉴定出一个额外的变体，该变体占8个分离株。高变区中的特定基序导致了高变类型之间的许多差异。
SzP蛋白似乎仅限于选定的几种类型。SzP蛋白的变异通常基于不同的基序而非随机的氨基酸取代来确定。SzP蛋白变异与马匹感染的临床表现之间似乎没有任何关联。
