Expression, purification, crystallization and X-ray diffraction studies of a novel root-induced secreted protein from Trichoderma virens

Target highlights in CASP14: Analysis of models by structure providers

The biological and functional significance of selected Critical Assessment of Techniques for Protein Structure Prediction 14 (CASP14) targets are described by the authors of the structures. The authors highlight the most relevant features of the target proteins and discuss how well these features were reproduced in the respective submitted predictions. The overall ability to predict three-dimensional structures of proteins has improved remarkably in CASP14, and many difficult targets were modeled with impressive accuracy. For the first time in the history of CASP, the experimentalists not only highlighted that computational models can accurately reproduce the most critical structural features observed in their targets, but also envisaged that models could serve as a guidance for further studies of biologically-relevant properties of proteins.

Structure-function analysis reveals Trichoderma virens Tsp1 to be a novel fungal effector protein modulating plant defence

Trichoderma virens colonizes roots and develops a symbiotic relationship with plants where the fungal partner derives nutrients from plants and offers defence, in return. Tsp1, a small secreted cysteine-rich protein, was earlier found to be upregulated in co-cultivation of T. virens with maize roots. Tsp1 is well conserved in Ascomycota division of fungi, but none of its homologs have been studied yet. We have expressed and purified recombinant Tsp1, and resolved its structure to 1.25 Å resolutions, from two crystal forms, using Se-SAD methods. The Tsp1 adopts a β barrel fold and forms dimer in structure as well as in solution form. DALI based structure analysis revealed the structure similarity with two known fungal effector proteins: Alt a1 and PevD1. Structure and evolutionary analysis suggested that Tsp1 belongs to a novel effector protein family. Tsp1 acted as an inducer of salicylic acid mediated susceptibility in plants, rendering maize plants more susceptible to a necrotrophic pathogen Cochliobolus heterostrophus, as observed using plant defence assay and RT-qPCR analysis.

Fluorescence spectroscopy and molecular docking analysis of the binding of Lactobacillus acidophilus GIM1.208 β-glucosidase with quercetin glycosides

Lactobacillus acidophilus is an important probiotic. The β-glucosidase produced by L. acidophilus GIM1.208 can transform quercetin glycosides of Rosa roxburghii Tratt to release quercetin and improve the functional activity of raw materials. Understanding the interaction and the characteristics of the two will lay a theoretical foundation for the site-directed transformation and functional application of the catalytic active site of enzymes. In our study, using the heterologously expressed and highly stable, purified L. acidophilus GIM1.208 BGL as the strain, the representative quercetin in β-glucosidase and Rosa roxburghii Tratt was preliminarily predicted and explored using ultraviolet-visible absorption spectroscopy. Fluorescence spectroscopy combined with molecular docking was used to determine the interaction characteristics of the glycoside substrates, rutin (Rut) and isoquercitrin (Iso). Results from molecular docking showed that Asp159, Arg56, Iso294, Phe292, and Gly25 were the main residues of β-glucosidase and Rut. Arg56 was found to be the most crucial residue of β-glucosidase and isoquercitrin; the interaction between Rut and Iso and β-glucosidase was mainly driven by hydrogen bonding. The combined free energy of β-glucosidase and Iso was found to be -182.10 kcal/mol, while that of β-glucosidase and Rut was -32.37 kcal/mol. The results of fluorescence spectroscopy showed that the fluorescence intensity of β-glucosidase decreased with an increase in Rut and Iso concentrations. This interaction made β-glucosidase quench endogenous fluorescence, which was static quenching. The binding constants of Rut and Iso with β-glucosidase were determined to be 0.50×10⁷ and 0.31×10⁷ L/mol, respectively, indicating that rutin had a stronger affinity when interacting with β-glucosidase. These findings were consistent with our prediction results determined using molecular docking studies.