Structural biology—plastic degradation by using wax worm saliva
Plastic waste management is a pressing ecological, social, and economic challenge that has looked to diverse chemical-biology strategies to facilitate biodegradation. In a new report now on Science Advances, Mercedes Spinola-Amilibia ...
Using cryo-electron microscopy (cryo-EM) the team analyzed the saliva of the microorganisms directly from the native source. Based on 3D reconstructions, they revealed the composition of the buccal secretions to belong to four hexamerins that can oxidize and degrade polyethylene.
Using cryo-EM data and X-ray analysis, they showed the proteins self-assemble into three macromolecular complexes with distinct structural differences to regulate their activity. The results indicated the possibilities of exploring the functionalities of hexamerins for biotechnological functions in vivo.
Experiments to identify the salivary protein composition—Demetra, Cibeles, Ceres and Cora
Using cryo-EM analysis, Spinola-Amilibia and colleagues first revealed the molecular organization and composition of the primary proteins found in the lepidopteran saliva. Mass spectroscopy data revealed the fraction to contain a mix of proteins belonging to the hexamerin/ phenoloxidase (PO) superfamily.
Due to the high molecular mass of the complexes formed by this protein type, the team directly analyzed the buccal secretions using cryo-EM as a first step to explore the 3D architecture and nature of plastic degradation. The results showed clean particles with good contrast. Sequencing based on the cryo-EM maps revealed four sub-populations made of different proteins, however, since the proteins were difficult to identify and their catalyst nature also yet unknown, they were named according to preceding work.
Cryo–electron microscopy (cryo-EM) analysis of G. mellonella saliva. The saliva was diluted and directly applied to carbon-coated cryo-EM grids. Single-particle analysis revealed that wax worm (ww) buccal secretion is composed of three main oligomeric complexes formed by four proteins. ptcls, particles; sym, symmetry. Credit: Science Advances, doi: 10.1126/sciadv.adi6813
Three-dimensional structures of the arylphorins Demetra and Cibeles. (A) Details of equivalent areas of different monomers in the reconstruction that show that the quality of the electron microscopy (EM) map allowed to differentiate and build the structures of Demetra and Cibeles. (B) Two orthogonal views of the 3:3 trimer of dimers formed by Demetra and Cibeles. Proteins are shown as surface representation and glycosylations as sticks. One monomer of each trimer is highlighted as solid surface. (C) Detailed view of a Demetra-Cibeles dimer (right). Inset: Close-up region showing the EM density and model of an oligosaccharide. (D) Crystal structure of the Cibeles homohexamer. Credit: Science Advances, doi: 10.1126/sciadv.adi6813
Cryo–electron microscopy (cryo-EM) reconstruction of Ceres. (A) Overall organization of the homohexamer. Protein depicted as surface and glycosylations as sticks. One of the six monomers is highlighted as solid surface. (B) Two views of a Ceres monomer. Metal ions shown as black spheres. Inset: Close-up view of the coordination of one of the metal ions. (C) Depiction of the elongated density (visualized at a threshold value of 0.020) found at the core of Ceres monomers and some of the surrounding residues. Credit: Science Advances, doi: 10.1126/sciadv.adi6813