Transcriptional repressor that controls expression of the genes required for the catabolism of sialic acids (PubMed:9864311, PubMed:12897000, PubMed:23935044). Represses expression of the nanATEK-yhcH, nanCMS and yjhBC operons. Acts by binding directly to the Nan box, a region of approximately 30 bp covering the promoter region (PubMed:23935044). N-acetylneuraminic acid (Neu5Ac) inactivates NanR by converting NanR oligomers to monomers. Homodimer (PubMed:12897000, PubMed:23935044). Might also form higher-order oligomers (PubMed:23935044). Belongs to the NanR family.