Structural and functional basis of bacteriophage K64-ORF41 depolymerase for capsular polysaccharide degradation of Klebsiella pneumoniae K64.

Capsule polysaccharide is an important virulence factor of Klebsiella pneumoniae (K. pneumoniae), which protects bacteria against the host immune response. A promising therapeutic approach is using phage-derived depolymerases to degrade the capsular polysaccharide and expose and sensitize the bacteria to the host immune system. Here we determined the cryo-electron microscopy (cryo-EM) structures of a bacteriophage tail-spike protein against K. pneumoniae K64, ORF41 (K64-ORF41) and ORF41 in EDTA condition (K64-ORF41EDTA), at 2.37 Å and 2.50 Å resolution, respectively, for the first time. K64-ORF41 exists as a trimer and each protomer contains a ß-helix domain including a right-handed parallel ß-sheet helix fold capped at both ends, an insertion domain, and one ß-sheet jellyroll domain. Moreover, our structural comparison with other depolymerases of K. pneumoniae suggests that the catalytic residues (Tyr528, His574 and Arg628) are highly conserved although the substrate of capsule polysaccharide is variable. Besides that, we figured out the important residues involved in the substrate binding pocket including Arg405, Tyr526, Trp550 and Phe669. This study establishes the structural and functional basis for the promising phage-derived broad-spectrum activity depolymerase therapeutics and effective CPS-degrading agents for the treatment of carbapenem-resistant K. pneumoniae K64 infections.

Microwave frequency performance and high magnetic anisotropy of nanocrystalline Fe70Co30-B films prepared by composition gradient sputtering.

The fabrication and high-frequency ferromagnetic performances of nanocrystalline Fe70Co30-B soft magnetic films were investigated. It is revealed that the composition gradient sputtering method dramatically improves the high-frequency soft magnetic properties of the as-prepared films. This method gives rise to almost a linearly-increased distribution of compositions and residual stress. As a result, a very high ferromagnetic resonance frequency up to 6.7 GHz, high uniaxial magnetic anisotropic field up to 450 Oe, and low magnetic loss were obtained in as-deposited samples, which are particularly in favor of the integration between magnetic films and microwave components.