Cargo protein of a type 2A encapsulin nanocompartment probably involved in sulfur metabolism. Cysteine desulfurases mobilize the sulfur from L-cysteine to yield L-alanine, an essential step in sulfur metabolism for biosynthesis of a variety of sulfur-containing biomolecules. [sulfur carrier]-H + L-cysteine = [sulfur carrier]-SH + L-alanine Encapsulated enzyme is 7-fold more active than encapsulated enzyme. kcat for encapulated enzyme is 67 sec(-1), for unencapsulated enzyme is 10 sec(-1). There are 1-2 copies of this protein in each type 2A encapsulin shell. Present in when grown in sulfur-containing media, induced 42-fold after 48 hours of sulfur starvation (at protein level). Has a disordered N-terminal domain of about 225 residues that functions as a cargo-loading domain (tested with GFP) and a conserved C-terminal cysteine desulfurase domain. The first 100 residues also function as a cargo-loading domain but not as well as the first 225 residues. No growth phenotype for a double srpI-cyd deletion mutant in the presence or absence of sulfur. Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. Csd subfamily.