Molecular characteristics and phyletic evolution of structural maintenance of chromosome (SMC) protein in Nosema ceranae

To analyze the molecular characteristics of structural maintenance of chromosome (SMC) protein in Nosema ceranae, identify conserved motifs and structural domains within SMC in N. ceranae and other species followed by phyletic evolution analysis, thus enriching basic information about N. ceranae SMC and offering a basis for further functional study.

Related software on Expasy website were utilized to predict and analyze physical and chemical property, signal peptide, phosphorylation site, secondary structure and tertiary structure of SMC. MEME software was employed to identify conserved motifs within SMC in N. ceranae and other species. TBtools software was used to identify structural domains within SMC. Based on SMC in N. ceranae and other species, phylogenetic tree was constructed with neighbor-joining method by Mega 11.0 software.

SMC contained 1 102 amino acids, the molecular formula was C₅₇₈₇H₉₄₁₈N₁₅₂₆O₁₇₇₁S₄₁, the relative molecular weight was approximately 130 020, the lipid solubility coefficient was 93.49, the isoelectric point was 8.28, the average hydrophilic coefficient was −0.740, the number of hydrophilic amino acids was more than that of hydrophobic amino acids, and there was no typical signal peptide. SMC contained 50 serine phosphorylation sites, 26 tyrosine phosphorylation sites and 28 threonine phosphorylation sites. It as well included 787 α-helix, 106 β-sheet, 49 β-turn, and 160 random coil. SMC were simultaneously localized in nucleus, cytoplasm and mitochondria. Furthermore, SMC in N. ceranae, Encephalitozoon hellem, Hamiltosporidium magnivora, Nosema granulosis, Thelohania contejeani, Piromyces finnis, Trichophyton interdigitale, Trichophyton violaceum, Trichophyton tonsurans and Aspergillus melleus all contained nine same conserved motifs and two structural domains such as SMC_N and SMC_hinge. Further investigation indicated that the similarity of amino acid sequences of SMC between N. ceranae and P. finnis was the highest (61.96%), while that between N. ceranae and T. contejeani was the lowest (34.73%); SMC in N. ceranae and N. granulosis were clustered into a branch with the confidence of 99%, and their evolutionary distance was the closest.

The results define the molecular characteristics of N. ceranae SMC and enrich basic information about SMC, disclose that SMC in N. ceranae and other microsporidia are highly consevative, and provide a basis for further functional study.