D9A

D9A is a protein variant notation used in biochemistry and molecular biology to indicate a specific amino acid substitution: the aspartic acid (D) at position 9 has been replaced by alanine (A) in the protein sequence. The designation is commonly seen in mutagenesis studies and in descriptions of mutant constructs.

In practice, D9A is used to probe the role of a given residue in protein function, structure, or interactions. It appears in naming conventions for mutant proteins (for example, a variant might be referred to as ProteinX–D9A). Because it conveys both the original residue and its position, the mutation helps researchers compare wild-type and altered forms across experiments and publications.

Biochemically, replacing aspartic acid with alanine removes a negatively charged side chain and reduces side-chain size at that position. The effects of a D9A substitution are highly context-dependent: it may disrupt catalytic activity, metal ion coordination, hydrogen bonding, substrate binding, or protein stability if the aspartate participates in these roles. Conversely, in regions where the aspartate is not functionally critical, the mutation may have little impact. The outcome is influenced by the protein’s overall fold, active site geometry, and interaction network.

Generation and analysis of a D9A variant typically involve site-directed mutagenesis to create the codon change, followed by sequencing to confirm the alteration. The mutant and wild-type proteins are then expressed and purified, and their properties are assessed through activity assays, stability measurements, binding studies, and structural analyses to determine the mutation’s impact. The interpretation depends on the specific protein and experimental context.