In silico design and in vitro validation of a novel PCR-RFLP assay for determination of phylogenetic clusters of streptokinase gene alleles in streptococci groups

Abstract

Streptokinase (SK), a heterogeneous plasminogen (Pg) activator protein secreted by groups A, C and G streptococci (GAS/GCS/GGS) is a virulence factor composed of three structural domains; SKα/SKβ/SKγ. Phylogenetic analysis of the major variable region of SKβ (sk-V1; nucleotides 448-791; 343bp) which classifies the SK alleles into SK1/SK2 clusters and SK2a/SK2b sub-clusters, is an approved assay to categorize clinical/natural streptococcal-isolates into co-related functional/pathogenesis groups. Herein, we describe a novel PCR-RFLP assay that in combination with Numerical Taxonomy and multivariate analysis System (NTSYS) resulted to dendrograms with complete adaption to that of the phylogenetic analysis of sk-V1-based clustering. In silico analyses by 30 restriction enzymes on GenBank-acquired sk-V1 sequences of known streptococcal clusters, resulted to the selection of "BsrI, MseI and Tsp45I″ enzymes that produced proper patterns to construct the expected dendrograms. In vitro analysis of the selected enzymes on clinical isolates of GAS/GCS/GGS validated the production of the same in silico-observed digestion patterns. Comparison of the constructed dendrogram and phylogenetic trees of selected GenBank and clinical isolates of streptococci indicated complete adaptation. Assessment of Pg-activation activity in selected clinical isolates indicated the expected co-related functionalities of the classified SK-clusters by the invented PCR-RFLP/NTSYS method. The simplicity of the assay relieves the need of sequencing/phylogenetic analyses for SK-clustering.

Keywords: Allelic variation; Gene clustering; Numerical taxonomy; Phylogenetic analysis; Streptokinase; Virulence factor.