Abstract:

Serine protease inhibitors, termed Serpins, bind and inhibit serine proteases that control central coagulation, immunity and connective tissue remodeling throughout the mammalian body. Genetic mutations in serpins including alpha-1 anti-trypsin, neuroserpin and anti-thrombin, cause severe disease ranging from emphysema and epilepsy to clotting disorders. With classic serpin inhibitory function there is cleavage of a reactive center loop (RCL) by selectively targeted proteases, forming a suicide complex with translocation of the protease to the opposite pole of the serpin, adding an additional A beta sheet sequence and forming inactive ‘suicide complexes’. In diseases caused by serpin mutations, there is RCL insertion into adjacent mutated serpin A beta sheet or binding at other sites. Large DNA viruses express serpins with highly potent immune and coagulation modifying activity, functioning at low doses with selective targeting of mammalian pathways, providing a new class of immune modulating biologics. Myxomavirus-derived Serp-1, effectively blocks immune disorders in a wide range of models, providing a new therapeutic class, improving outcomes when given systemically at low doses (microgram/kg range). In a pristane induced lupus lung hemorrhage model, PEGylated (PEGSerp-1) reduces lung hemorrhage and inflammation. Immunoprecipitation and mass spectrometry analysis demonstrated binding of PEGSerp-1 to known target proteases, inflammatory mediators and unexpectedly to selected mammalian serpins. Here we examine serpin-to-serpin interactions, specifically PEGSerp-1 binding to unrelated mammalian serpins in vivo, in vitro and in silico. We postulate a new, previously unexplored, regulatory serpinosome complex.

Keywords: Serpins, PEGylated Serp-1, Pulmonary inflammation, Immune modulation, Serpin-to-serpin interactions, Lupus lung hemorrhage, Therapeutic biologics