TpPL7A and TpPL7B, members of CAZy family PL7, act as β-glucuronan lyases. TpPL7A diverges by lacking the catalytic histidine, identified as the Brønsted base in PL7 alginate lyases. Our research, including TpPL7A's crystal structure, and mutagenesis studies, reveals a shared syn-β-elimination mechanism with a single tyrosine serving as both base and acid catalyst. This mechanism may extend to subfamily PL7_4 glucuronan lyases.