Amino R, Porto R M, Chammas R, Egami M I, Schenkman S
Departamento de Microbiologia, Imunologia e Parasitologia, Escola Paulista de Medicina, UNIFESP, São Paulo, S. P. 04023-062, Brazil.
J Biol Chem. 1998 Sep 18;273(38):24575-82. doi: 10.1074/jbc.273.38.24575.
Sialidases (EC 3.2.1.18) are commonly found in viruses, bacteria, fungi, protozoa, and vertebrates, but not in invertebrates. We have previously reported the presence of a new sialidase activity in the gut of exclusively hematophagous insects of the Triatoma genus, which transmit Chagas' disease (Amino, R., Acosta, A., Morita, O. M., Chioccola, V. L. P., and Schenkman, S. (1995) Glycobiology 5, 625-631). Here we show that this sialidase is present in the salivary gland of Triatoma infestans, and it is released with the saliva during the insect bite. The sialidase was purified to homogeneity (>5000 times) to a specific activity of more than 20 units/mg. It elutes from a gel filtration column with a volume corresponding to the size of 33 kDa, and it migrates as a single 26-kDa band in SDS-polyacrylamide gel electrophoresis, which is unusually smaller when compared with other known sialidases. T. infestans sialidase hydrolyzes preferentially alpha2-->3-linked sialic acids at pH 4-8, with maximal activity between pH 5.5 and 6.5, which is compatible with the optimal pH of secreted sialidases. The sialidase is competitively inhibited by 2-deoxy-2, 3-dehydro-N-acetyl-neuraminic acid (Ki = 0.075 mM) and differently from many sialidases, with exception of Salmonella typhimurium sialidase, it is inhibited competitively by HEPES (Ki = 15 mM). The fact that T. infestans sialidase is released with the saliva and can hydrolyze sialyl-LewisX blood groups, which are the ligands for selectins, suggests that it might have a role in the blood feeding.
唾液酸酶（EC 3.2.1.18）常见于病毒、细菌、真菌、原生动物和脊椎动物中，但在无脊椎动物中不存在。我们之前报道过，在传播恰加斯病的锥蝽属专性吸血昆虫的肠道中存在一种新的唾液酸酶活性（Amino, R., Acosta, A., Morita, O. M., Chioccola, V. L. P., and Schenkman, S. (1995) Glycobiology 5, 625 - 631）。在此我们表明，这种唾液酸酶存在于侵扰锥蝽的唾液腺中，并且在昆虫叮咬时会随唾液释放出来。该唾液酸酶被纯化至同质（>5000倍），比活性超过20单位/毫克。它从凝胶过滤柱中洗脱时的体积对应于33 kDa的大小，并且在SDS - 聚丙烯酰胺凝胶电泳中迁移为一条单一的26 kDa条带，与其他已知的唾液酸酶相比异常小。侵扰锥蝽唾液酸酶在pH 4 - 8时优先水解α2→3连接的唾液酸，在pH 5.5至6.5之间活性最高，这与分泌型唾液酸酶的最佳pH值相符。该唾液酸酶受到2 - 脱氧 - 2,3 - 脱氢 - N - 乙酰神经氨酸的竞争性抑制（Ki = 0.075 mM），并且与许多唾液酸酶不同，除了鼠伤寒沙门氏菌唾液酸酶外，它受到HEPES的竞争性抑制（Ki = 15 mM）。侵扰锥蝽唾液酸酶随唾液释放且能水解作为选择素配体的唾液酸化路易斯X血型这一事实表明，它可能在取食血液过程中发挥作用。
