Catalyzes the conversion of 3-dehydroshikimate to protocatechuate (3,4-dihydroxybenzoate), a common intermediate of quinate and shikimate degradation pathways. Is required for growth on either quinate or shikimate as a sole carbon source. 3-dehydroshikimate = 3,4-dihydroxybenzoate + H2O Requires a divalent metal cation for DSD activity, with a preference for Co(2+) but can also use Ni(2+), Mn(2+) and Mg(2+). Aromatic compound metabolism; 3,4-dihydroxybenzoate biosynthesis. Homodimer. Consists of a fusion of two distinct domains: an N-terminal sugar phosphate isomerase-like domain associated with DSD activity and a C-terminal hydroxyphenyl-pyruvate dioxygenase-like domain. This C-terminal domain does not show any 4-hydroxyphenylpyruvate dioxygenase (HPPD) or protocatechuate dioxygenase (PCD) activity, but appears to be important for optimal DSD activity of QuiC1 in vivo. While wild-type P.aeruginosa grows readily on either quinate or shikimate as a sole carbon source, the knockout strain does not efficiently utilize these substrates. Growth of the knockout is enhanced by the addition of protocatechuate, bypassing the function of QuiC1. Belongs to the bacterial two-domain DSD family.