Human amnionless (AMN) is necessary for efficient absorption of vitamin B12. Defects in AMN is a cause of recessive hereditary megaloblastic anemia 1 (RH-MGA1), also known as MGA1 Norwegian type or Imerslund-Grasbeck syndrome (I-GS)[]. AMN may direct the production of trunk mesoderm during development by modulating a bone morphogenetic protein (BMP) signaling pathway in the underlying visceral endoderm [, ].
AMP nucleosidase (AMN) catalyses the hydrolysis of AMP to form adenine and ribose 5-phosphate. It is only found in prokaryotes, where it plays a role in purine nucleoside salvage and intracellular AMP level regulation []. The gene for AMP nucleosidase from Escherichia coli (amn) encodes a protein of 483 amino acids. A comparison of the amino acid sequence for AMP nucleosidase with that for yeast AMP deaminase shows that there is a region where only six out of eight amino acids are identical but there is no other overall homology. AMN also showed little similarity to consensus sequences for adenylate binding sites even though the enzyme is known to have a catalytic site for AMP and regulatory sites for MgATP and phosphate [].The enzyme is a homohexamer, and each monomer has two domains: a catalytic domain and a putative regulatory domain. The overall topology of the catalytic domain and some features of the substrate binding site resemble those of the nucleoside phosphorylases. The structure of the regulatory domain consists of a long helix and a four-stranded sheet, but has a novel topology []. The majority of sequences in this entry are annotated as AMP nucleosidase. Their taxonomic range is restricted to the Bacteroidetes and Chlamydiae.
AMP nucleosidase (AMN) catalyses the hydrolysis of AMP to form adenine and ribose 5-phosphate. It is only found in prokaryotes, where it plays a role in purine nucleoside salvage and intracellular AMP level regulation []. The gene for AMP nucleosidase from Escherichia coli (amn) encodes a protein of 483 amino acids. A comparison of the amino acid sequence for AMP nucleosidase with that for yeast AMP deaminase shows that there is a region where only six out of eight amino acids are identical but there is no other overall homology. AMN also showed little similarity to consensus sequences for adenylate binding sites even though the enzyme is known to have a catalytic site for AMP and regulatory sites for MgATP and phosphate [].The enzyme is a homohexamer, and each monomer has two domains: a catalytic domain and a putative regulatory domain. The overall topology of the catalytic domain and some features of the substrate binding site resemble those of the nucleoside phosphorylases. The structure of the regulatory domain consists of a long helix and a four-stranded sheet, but has a novel topology [].
