EXAFS evidence for a "cysteine switch" in the activation of prostromelysin

Zn K-edge EXAFS data of the matrix metalloproteinase (MMP) stromelysin-I were obtained in both its latent proenzyme and mature active forms. The Fourier-filtered (back-transform 0.7-2.3 angstrom) (chi)k3 spectrum of mature stromelysin was satisfactorily simulated with 4 N/O scatterers per Zn at 2.01 angstrom, while similar fits for prostromelysin were judged unacceptable because of unreasonable Debye-Waller factors or significantly larger residuals of the fits. For prostromelysin, excellent fits were obtained with the introduction of a sulfur scatterer at 2.25 angstrom. These data provide the first direct evidence for the coordination of zinc by the sole cysteine in the N-terminal domain of prostromelysin and confirm that the cysteine is lost upon activation. These results provide support for a "cysteine switch" structural model for MMP proenzymes that suggests the interaction of the conserved propeptide cysteine with zinc is present in the latent form. Examination of the Zn-S bond length and outer shell carbon contributions suggests that the 2 g-atoms of zinc recently shown to be present in stromelysin (Salowe, S. P., et al. Biochemistry 1992, 31, 4535-4540) reside in independent zinc sites.