Here's the full sequence of the protein, found in the supplement [1]

KSSEPASVSAAERRAETEQHKLEQENPGIVWLDQHGRVTAENDVALQILGPAGEQSLGVAQDSLEGIDVVQLHPEKSRDKLRFLLQSKDVGGSPVKSPPPVAMMINIPDRILMIKVSSMIAAGGASGTSMIFYDVTDLTTEPSGLPAGGSAPSHHHHHH

It is a protein encoding the PxRcoM-1 heme binding domain with C94S mutation and a C-terminal 6xHis tag (RcoM-HBD-C94S)

[1] https://www.pnas.org/doi/10.1073/pnas.2501389122#supplementa...