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NH2-terminal sequence of macrophage-expressed natural resistance-associated macrophage protein (Nramp) encodes a
C H Barton1, J K White, T I Roach
1Department of Medicine, University of Cambridge Clinical School, Addenbrooke's Hospital, United Kingdom.
Abstract:
The Lsh/Ity/Bcg locus on mouse chromosome 1 regulates macrophage (m phi) priming/activation for antimicrobial activity against intracellular pathogens. A candidate Bcg gene, designated natural resistance-associated m phi protein (Nramp), recently isolated from a pre-B cell cDNA library encodes a polytopic integral membrane protein with structural features common to prokaryotic and eukaryotic transporters. In the present study, an activated m phi cDNA library yielded new Nramp clones that differ in the 5' region from the published pre-B cell-derived clone sequence, resulting in addition of 64 amino acids at the NH2 terminus of the predicted protein. This new domain is rich in proline, serine, and basic amino acids, and includes three protein kinase C phosphorylation sites and a putative Src homology 3 binding domain. RNAs containing this domain are the only form found in the m phi. Hence, the protein encoded by this RNA is the candidate molecule mediating natural resistance to intra-m phi pathogens.
Insights
Researchers identified a new Nramp protein variant in macrophages, crucial for fighting intracellular pathogens. This variant, with added amino acids, is key to natural resistance in macrophages.
Area of Science:
- Immunology
- Genetics
- Cell Biology
Background:
- The Lsh/Ity/Bcg locus on mouse chromosome 1 is vital for macrophage (m phi) activation against intracellular pathogens.
- A candidate gene, natural resistance-associated m phi protein (Nramp), was previously identified and encodes a membrane transporter.
Purpose of the Study:
- To identify and characterize novel Nramp variants expressed in activated macrophages.
- To elucidate the molecular basis of natural resistance to intracellular pathogens mediated by Nramp.
Main Methods:
- Construction and screening of an activated macrophage cDNA library.
- Sequence analysis of novel Nramp clones.
- Bioinformatic analysis of protein domains and phosphorylation sites.
Main Results:
- New Nramp clones were isolated from an activated macrophage cDNA library.
- These clones contain a distinct 5' region compared to the pre-B cell clone, adding 64 amino acids to the N-terminus.
- The novel N-terminal domain is rich in proline, serine, and basic amino acids, featuring protein kinase C phosphorylation sites and a Src homology 3 binding domain.
- RNA transcripts encoding this extended Nramp variant are exclusively found in macrophages.
Conclusions:
- The newly identified Nramp variant, expressed in macrophages, is the likely candidate molecule responsible for natural resistance to intracellular pathogens.
- The unique N-terminal domain likely plays a critical role in macrophage function and pathogen resistance.