人核糖核酸酶(RNase) 3,6,7属于RNase A超家族，在感染时分泌，与细菌细胞膜相互作用(Torrent M et al. 2010;Pulido D等。2016a, b)。
RNase A家族是脊椎动物特有的基因家族(Goo SM & Cho S 2013)。RNase A家族成员具有序列同源性的特定元素，独特的二硫键合三级结构，以及水解聚合RNA的能力(Beintema JJ & Kleineidam RG 1998;Rosenberg HF 2008)。在人类中发现了8种催化活性成员:RNase1(胰腺RNase)， RNase2(嗜酸性粒细胞源性神经毒素/EDN)， RNase3(嗜酸性粒细胞阳离子蛋白/ECP)， RNase4, RNase5(血管生成素)，RNase6, RNase7(皮肤源性RNase)，和RNase8 (RNase7的扩散paralog) (Sorrentino S 2010)。对人类基因组序列的分析揭示了另外5种被命名为RNases 9-13的rna酶的存在，尽管它们似乎失去了酶活性(Devor EJ et al. 2004;Castella S et al. 2004;Cho S et al. 2005)。所有人RNase A家族成员都编码相对较小的14至16kDa的多肽，包含20至28个氨基酸的信号肽，用于蛋白质分泌。成熟的rnase含有6 - 8个半胱氨酸残基，这对于维持整个三级结构至关重要(Sorrentino S 2010)。除了核糖核酸酶活性外，RNase A家族成员还涉及多种生物活性，包括抗病原体和免疫调节活性(Harder J & Schroder JM 2002; Rudolph B et al. 2006; Boix E et al. 2008; Boix and Nogués, 2007; Spencer JD et al. 2011; Becknell B et al. 2015; Rosenberg HF 2015). Evidence of antimicrobial properties displayed by distantly related members ascribed to the family an ancestral role in host defence (Pizzo E & D’Alessio G 2007; Rosenberg HF et al. 2008).
RNase3、RNase6和RNase7已被确定为最有效的人类抗菌核糖核酸酶，对革兰氏阳性和革兰氏阴性细菌具有广泛的抗菌作用(Pulido D等人，2013,2016;张杰等。2003;Boix E et al. 2008;Torrent M et al. 2010)。突变分析显示，RNase7蛋白对铜绿假单胞菌、粪肠杆菌和大肠杆菌具有与野生型蛋白相似的抑菌活性，表明RNase7可能独立于其核糖核酸酶催化活性而杀灭细菌(Huang YC et al. 2007;Koten B et al. 2009)。核糖核酸酶失活的RNase3和6蛋白对金黄色葡萄球菌的杀微生物作用也有类似的报道(Rosenberg HF 1995;Pulido D et al. 2016a)。RNase3、6和7作为高pI的阳离子蛋白，与生物膜的阴离子组分相互作用(Zhang J et al. 2003;Boix E et al. 2008; Torrent M et al. 2010; Boix E et al. 2012; Pulido D et al. 2016a). RNase3, 6 and 7 present, respectively, a high number of either Arg, His or Lys surface-exposed residues that may contribute to their distinct bactericidal mechanisms of action (Torrent M et al. 2010; Prats-Ejarque G et al. 2016). RNase3 displays a membrane disruption capacity that is dependent on both surface exposed hydrophobic and cationic residues. RNase3 can bind and partially insert into the lipid bilayers, promoting its aggregation and final lysis, following a carpet-like mechanism. The RNase3 agglutination process precedes the bacterial death and lysis event. The antimicrobial properties of the RNase6 are comparable to its RNase3 homolog and correlate to the bacterial cell damage and agglutination activities (Pulido D et al. 2016a). In contrast, RNase7 has no significant membrane aggregation capacity (Torrent M et al. 2010). RNase7 binds and permeabilizes the bacterial membrane displaying a much higher leakage capacity compared to RNase3 (Torrent M et al. 2010; Huang YC et al. 2007). Membrane permeabilization by RNase7 required four clustered lysine residues but no catalytic residues (Huang YC et al. 2007). Binding to PGN and LPS has been reported for RNases 3 and 7 (Torrent M et al. 2010; Pulido D et al. 2016b). Studies using a battery of progressively truncated LPS-defective E. coli strains correlated the LPS interaction with the protein cell agglutination and bactericidal activities (Pulido D et al. 2012). Further work indicated that RNase3 and RNase 6 high cell agglutination activity towards Gram negative species is retained by their respective N-terminus peptides (Torrent M et al. 2012, 2013; Pulido D et al. 2016c). In particular, the RNase3 N-terminus encompasses a specific patch (Y33-R36) required for LPS binding and an hydrophobic aggregation prone region (A8-I16) that mediates the protein self amyloid- like aggregation and promotes the cell death.
