Catalyzes the decarboxylation of L-aspartate to produce beta-alanine, and the decarboxylation of L-glutamate to produce 4-aminobutanoate. Can also use cysteate and, to a lesser extent, cysteine sulfite (3-sulfino-L-alanine), but not L-tyrosine. Specific activities toward L-aspartate and cysteate are higher than toward L-glutamate. H(+) + L-aspartate = beta-alanine + CO2 H(+) + L-glutamate = 4-aminobutanoate + CO2 H(+) + L-cysteate = CO2 + taurine 3-sulfino-L-alanine + H(+) = CO2 + hypotaurine kcat is 0.34 sec(-1) with L-aspartate as substrate. kcat is 0.26 sec(-1) with L-glutamate as substrate. kcat is 0.65 sec(-1) with cysteate as substrate. kcat is 0.03 sec(-1) with cysteine sulfite as substrate. Optimum pH is 8.0 with glutamate as substrate. Optimum temperature is higher than 97 degrees Celsius with glutamate as substrate. Cofactor biosynthesis; coenzyme A biosynthesis. Monomer. Belongs to the group II decarboxylase family. MfnA subfamily.