%0 Journal Article
%T Cooperative binding of calcium ions modulates the tertiary structure and catalytic activity of Matrix-Metalloproteinase-9
%A Shakila Tobwala
%A D. K. Srivastava
%J Advances in Enzyme Research
%P 17-29
%@ 2328-4854
%D 2013
%I Scientific Research Publishing
%R 10.4236/aer.2013.12002
%X To ascertain the molecular basis of Ca2+-mediated activation of matrix metalloproteinase-9 (MMP-9), we determined the accessibility of tryptophan residues to externally added acrylamide as quencher in the absence and presence of the metal ion. The steady-state and time resolved fluorescence data revealed that MMP-9 possesses two classes of tryptophan residues, ¡°exposed¡± and ¡°buried¡± which are quenched by the collisional rate constants (kq) of 3.2¡ä 109M-1.s-1 and 7.5¡ä 108M-1.s-1, respectively. These values are impaired by approximately two and three-fold, respectively, in the presence of 10 mM Ca2+. The Stern-Volmer constants (Ksv values) predicted from the time resolved fluorescence data (in the absence of Ca2+ ) satisfied the dynamic quenching model of the enzyme¡¯s tryptophan residues. This was not the case in the presence of Ca2+ ; the steady-state acrylamide quenching data could only be explained by a combination of ¡°dynamic¡± and ¡°static¡± quenching models. A cumulative account of these data led to the suggestion that the binding of Ca2+ modulated the tertiary structure of the protein by decreasing the dynamic flexibility of the enzyme, which is manifested in further structuring of the enzyme¡¯s active site pocket toward facilitating catalysis. Arguments are presented that the binding of Ca2+ at distal sites ¡°dynamically¡± communicates with the
active site residues of MMP-9 during catalysis.
%K Matrix Metalloproteinase-9
%K Gelatinase-B
%K Fluorescence Lifetime
%K Quenching
%K Acrylamide
%K Stern-Volmer Constant
%U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=33419