Induction of conformational changes within crystals of plasminogen activator inhibitor-1 (PAI-1)

Plasminogen activator inhibitor-1 (PAI-1) is a member of the serpin (serine protease inhibitor) superfamily, that can adopt three different conformati ons: active, latent and substrate. It was recently shown that the non-ionic detergent Triton X-100 (TX-100) can accelerate the conformational transiti ons in wild-type PAI-I in solution. Recently, we have crystallized a stable PAI-1 variant (PAI-l-stab) in its active conformation (Acta Cryst D 55, 57 4-576, 1999). in this study, we examined the effect of TX-100 on the confor mational transitions in PAI-1-stab, in solution as well as in crystals. Wit hin the crystal (at t = 0: 75 +/- 3% active, 10 +/- 4% non-reactive and 15 +/- 4% substrate; mean +/- SD, n = 3) a time-dependent increase of the subs trate form was observed, with a concomitant decrease of the active form. A steady state situation with active (52 +/- 2%) and substrate (34 +/- 5%) fo rms was reached within 4 h. Under those conditions, the amount of non-react ive PAI-I remained essentially unchanged (14 +/- 5%). The conformational ch anges induced by TX-100 in PAI-1-stab in solution (at t = 0: 59 +/- 2% acti ve, 0% non-reactive and 41 +/- 2% substrate, n = 3) were characterized main ly by a decrease of the active form in favour of the non-reactive form, rea ching a steady state between 15 and 24 h resulting in active (20 +/- 3%, n = 4), substrate (29 +/- 3%) and non-reactive (48 +/- 5%) forms. Thus, this study demonstrates that, even though characterized with a restri cted mobility, conformational changes can be induced within protein crystal s. Importantly, in both cases studied a steady state situation with various functional forms was observed. (C) 1999 Hartcourt Publishers Ltd (C) Harco urt Publishers Ltd 1999.