2-Amino-3-nitro-pyridinium 4-hy-droxy-benzene-sulfonate.

In the crystal structure of the title salt, C(5)H(6)N(3)O(2) (+)·C(6)H(5)O(4)S(-), N-H⋯O and O-H⋯O hydrogen bonds link the cations and anions. The dihedral angle between the rings of the cation and anion is 79.91 (6)°.

Mechanistic insight into the function of the C-terminal PKD domain of the collagenolytic serine protease deseasin MCP-01 from deep sea Pseudoalteromonas sp. SM9913: binding of the PKD domain to collagen results in collagen swelling but does not unwind the collagen triple helix.

Deseasin MCP-01 is a bacterial collagenolytic serine protease. Its catalytic domain alone can degrade collagen, and its C-terminal PKD domain is a collagen-binding domain (CBD) that can improve the collagenolytic efficiency of the catalytic domain by an unknown mechanism. Here, scanning electron microscopy (SEM), atomic force microscopy (AFM), zeta potential, and circular dichroism spectroscopy were used to clarify the functional mechanism of the PKD domain in MCP-01 collagenolysis.