Interaction between rat serum phosphorylcholine binding protein and platelet activating factor

The binding of rat serum phosphorylcholine binding protein (PCBP) to platelet activating factor (PAF) has been demonstrated using a HPLC-gel filtration technique. The bulk of the bound [3H]-PAF eluted with a higher molecular weight species of PCBP, possibly an aggregated form of PCBP. A smaller amount of [3H]-PAF co-eluted with the major monomeric species of PCBP. Formation of the PCBP-PAF complex was calcium dependent and could be inhibited by phosphorylcholine, suggesting the involvement of the phosphorylcholine binding site on PCBP. Binding of albumin and alpha 1-acid glycoprotein to PAF was not affected by phosphorylcholine or calcium. The specificity of this binding may explain the inhibitory effect of PCBP and related phosphorylcholine binding proteins on PAF induced aggregation of platelets.     

Interaction between the RP4 coupling protein TraG and the pBHR1 mobilization protein Mob

It is currently believed that interaction between the relaxosome of a mobilizable plasmid and the transfer machinery of the helper conjugative plasmid is mediated by a TraG family coupling protein. The coupling proteins appear as an essential determinant of mobilization specificity and efficiency. Using a two-hybrid system, we demonstrated for the first time the direct in vivo interaction between the coupling protein of a conjugative plasmid (the TraG protein of RP4) and the relaxase of a mobilizable plasmid (the Mob protein of pBHR1, a derivative of the broad host range plasmid pBBR1). This interaction was confirmed in vitro by an overlay assay and was shown to occur even in the absence of the transfer origin of pBHR1. We showed that, among 11 conjugative plasmids tested, pBHR1 is efficiently mobilized only by plasmids encoding an IncP-type transfer system. We also showed that the RP4 TraG coupling protein is essential for mobilization of a pBBR1 derivative and is the element that allows its mobilization by R388 plasmid (IncW) at a detectable frequency.