Inactivation of N-TIMP-1 by N-terminal acetylation when expressed in bacteria

The high-affinity binding of tissue inhibitors of metalloproteinases (TIMPs) to matrix metalloproteinases (MMPs) is essential for regulation of the turnover of the extracellular matrix during development, wound healing, and progression of inflammatory diseases, such as cancer, atherosclerosis, and arthritis. Bacterially expressed N-terminal inhibitory domains of TIMPs (N-TIMPs) have been used extensively for biochemical and biophysical study of interactions with MMPs. Titration of N-TIMP-1 expressed in E. coli indicates, however, that only about 42% of the protein is active as an MMP inhibitor. The separation of inactive from fully active N-TIMP-1 has been achieved both by MMP affinity and by high-resolution cation exchange chromatography at an appropriate pH, based on a slight difference of charge. Purification by cation exchange chromatography with a Mono S column enriches the active portion of N-TIMP-1 to >95%, with K(i) of 1.5 nM for MMP-12. Mass spectra reveal that the inactive form differs from active N-TIMP-1 in being N-terminally acetylated, underscoring the importance of the free alpha-NH(2) of Cys1 for MMP inhibition. N(alpha)-acetylation of the CTCVPP sequence broadens the N-terminal sequence motifs reported to be susceptible to alpha-amino acetylation by E. coli N-acetyl transferases.