AFFINITY BINDING OF A VAMPIRE BAT PLASMINOGEN-ACTIVATOR TO SEC RESINS

DSPA alpha 1 is a recombinant form of the vampire bat plasminogen acti vator which we have produced in mammalian cell culture. During the dev elopment of a recovery process for DSPA alpha 1 we observed an unexpec ted binding interaction between this protein and several types of gel filtration chromatography resins. Under typical operating conditions u sing neutral pH buffers, we found that DSPA flows through the sizing r esin and is fractionated, as expected, according to its molecular size . However, DSPA applied under certain acidic conditions (< pH 3) binds tightly to the Sephacryl series of resins. The protein is not release d until solvent conditions are changed, specifically the pH is raised above 3, From the results presented we conclude that this unexpected i nteraction with the gel filtration media is not simply an ion exchange nor a hydrophobic interaction, but rather a more complex, mixed mode ''affinity'' like binding. Several structural features of the DSPA pro tein which may be involved in this unique binding have been examined, including binding after inactivation of its active site, chemical degl ycosylation, chemical denaturation, or limited proteolysis. The ''affi nity'' interactions persist despite these treatments and lead us to co nclude that there may be a unique peptide sequence(s) within the prote in which is responsible for the binding interaction to Sephacryl resin s. (C) 1998 Academic Press.