Bioinformatic analyses of two defensin-like proteins from Silybum marianum flowers.

AGUSTINA FERNANDEZ; CONSTANZA LIGGIERI; MARIA LAURA COLOMBO; LAURA SUSANA BAKÁS; SANDRA ELIZABETH VAIRO CAVALLI

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de BioCiencias LIII Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2017

Sociedades de BioCiencias

Plant defensins and defensin-like proteins (DEFL) are small, basic, cysteine-richproteins of the innate defence system with a conserved tertiary structure ?thecysteine stabilized α/β motif? encompassing a loop named γ-core connectingtwo β-strands linked to antifungal activity. We cloned and predicted the tertiarystructure of two DEFL from Silybum marianum flowers (DefSm1D and DefSm2),we also compared both DEFL at sequence and structure level as well asperformed a functional analysis based on the predicted structures. Both DEFLare 54 aminoacid proteins with 63% sequence identity, estimated masses ca. 6kDa and pI above 8.5 (Compute pI/Mw tool). Analysis of both γ-core sequencesrevealed the presence of 3 and 4 positive residues, respectively, probablyrelated to interaction with negative charges on target membrane and/orpathogen cell wall. Structural models of DefSm1D and DefSm2 were built usingMODELLER v9.14 based on Artv1 (PDB: 2KPY) and Ah-AMP1 (PDB: 1BK8)crystal structure; templates were found with HHPred fold assignment method.Comparative analysis of structural models (RCSB PDB Protein ComparisonTool) revealed that sequence variation between DEFL had an effect on theoverall structure of these peptides with a global RMSD (root-mean-squaredeviation) difference of 2.33 Å. Structural models functional analysis (ProFuncserver) showed that both defensins share significant results for extracellularcomponent; defence, stress, and biotic stimulus response; killing of cells fromanother organism and antifungal response. Structural models electrostaticsurface potential calculated solving the Poisson-Boltzmann equation (PBEQSolver) show a surface charge distribution that endows peptides withamphipathicity, which would allow them to interact with the pathogen's cellmembrane. Both DEFL share a well conserved tertiary structure but variability inprimary amino acid sequence that can change the activity spectrum exhibitedby these closely related proteins.