N-terminal asparagine deamidase that mediates deamidation of N-terminal asparagine residues to aspartate. Required for the ubiquitin-dependent turnover of intracellular proteins that initiate with Met-Asn. These proteins are acetylated on the retained initiator methionine and can subsequently be modified by the removal of N-acetyl methionine by acylaminoacid hydrolase (AAH). Conversion of the resulting N-terminal asparagine to aspartate by NTAN1 renders the protein susceptible to arginylation, polyubiquitination and degradation as specified by the N-end rule. This enzyme does not act on substrates with internal or C-terminal asparagines and does not act on glutamine residues in any position (By similarity). Does not seems to be involved in immune response, unlike the N-terminal glutamine amidohydrolase NTAQ1 (PubMed:30117535). H(+) + H2O + N-terminal L-asparaginyl-[protein] = N-terminal L-aspartyl-[protein] + NH4(+)