The immunodominant antigen A, IsaA, of Staphylococcus aureus was found to include a putative soluble lytic transglycosylase domain in its C-terminal region. Since the presence of this distinctive domain suggested that the protein might participate in peptidoglycan turnover, as indicated in Gram-negative bacteria, its cellular location was investigated. The protein was found not only in the culture supernatant but also in the cell wall fraction. To estimate its physiological role for the bacterium, its cell surface distribution was studied by immunoelectron microscopy. Protein A-gold particles binding to the immune complex were mainly located on the septal region of the bacterial cell surface. These data suggested that IsaA might be involved in bacterial cell separation through a preferential interaction with peptidoglycan chain.

No abstract

Innate immunity is the front line of self-defense against microbial infection. After searching for natural compounds that regulate innate immunity using an ex vivo Drosophila culture system, we identified a new cyclic depsipeptide, aspergillicin F, from the fungus Aspergillus sp., as an innate immune suppressor. The total synthesis and biological evaluation of the aspergillicin family, including aspergillicin F, were performed, revealing that slight structural differences in the side chains of amino acid residues alter innate immunity-regulating activity.

The existence of a second binding site to Staphylococcus aureus on fibronectin was explored by using a recombinant protein, alb-FnBPA, which was obtained from an Escherichia coli clone containing a part of the gene for fibronectin-binding protein of S. aureus. Limited digestion with trypsin produced a 215K fragment from the B chain of fibronectin by releasing an N-terminal 32 kDa region. This C-terminal large fragment captured alb-FnBPA in spite of lacking the N-terminal binding region to S. aureus. This treatment also produced a 185K fragment from A chain by releasing N-terminal 32 kDa and C-terminal 37 kDa regions, and the 185K fragment possessed no binding ability. Thermolysin digestion was also performed to investigate the effect on the binding of releasing the C-terminal region from both of the chains and to locate the binding region to alb-FnBPA on the tryptic 215K fragment. But this digestion produced no fragment binding to alb-FnBPA except for the N-terminal 24K and its transient precursory fragments. These results indicate that both the N-terminal and the C-terminal regions of fibronectin bind to S. aureus, and suggest that the binding appears to involve cooperation between type III repeats and C-terminal type I repeats.

Branchiibius hedensis gen. nov., sp. nov., an actinobacterium isolated from a Japanese codling (Physiculus japonicus)