Histidine decarboxylase of Lactobacillus 30a. Comparative sequences of the beta chain from wild type and mutant enzymes.

Manual and automated sequencing of peptides isolated from tryptic, chymotryptic, and Staphylococcus aureus V8 protease digests of the beta chain of histidine decarboxylase from Lactobacillus 30a have established the following sequence for the wild type protein: NH2-Ser-Gly-Leu-Asp-Ala-Lys-Leu-Asn-Lys-Leu-Gly-Val-Asp-Arg-Ile-Ala-Ile-Ser-Pro -Tyr-Lys-Gln-Trp-Thr-Arg-Gly-Tyr-Met-Glu-Pro-Gly-Asn-Ile-Gly-Asn-Gly-Tyr-Val-Thr-Gly-Leu-Lys-Val-Asp-Ala-Gly-Val-Arg-Asp-Lys-Ser-Asp-Asp-Asp-Val-Leu-Asp-Gly-I le-Val-Ser-Tyr-Asp-Arg-Ala-Glu-Thr-Lys-Asn-Ala-Tyr-Ile-Gly-Gln-Ile-Asn-Met-Thr- Thr-Ala-Ser-COOH The beta chain from mutant 3 of this organism shows two amino acid replacements: Ser-51 is replaced by Ala and Gly-58 by Asp. These amino acid replacements result in a significant increase in the predicted alpha-helical content and a significant decrease in the isoelectric point of the mutant beta chain and are consistent with changes in physical and catalytic properties of the mutant histidine decarboxylase. In addition, about 15% of the mutant chains contain Met-Ser at the NH2 terminus rather than Ser. Asn-35 is partially deamidated in both proteins. Structural comparisons show that the histidine decarboxylase from Lactobacillus 30a and a similar pyruvoyl enzyme from Micrococcus sp. n. have evolved from a common ancestral protein.