ManX (EIIAB-Man) - Research Notes

Summary

ManX (P69797) is the cytoplasmic EIIAB phosphorylating subunit of the mannose-specific PTS in E. coli K12. It is encoded by the manXYZ operon (b1817).

Key findings

Domain structure and phosphorylation

• ManX is a bifunctional protein with N-terminal EIIA domain (residues 2-124) and C-terminal EIIB domain (residues 157-320), connected by a flexible hinge PMID:2681202
• EIIA domain is phosphorylated by HPr at His-10 (tele-phosphohistidine) [PMID:2681202, PMID:8262947]
• EIIB domain is phosphorylated at His-175 (pros-phosphohistidine) by EIIA [PMID:2681202, PMID:8262947]
• His-86 is involved in phosphoryl transfer between domains PMID:8262947

Dimerization

• ManX forms stable homodimers PMID:2999119
• H10C mutation abolishes dimerization PMID:8262947
• NMR structure of IIAMan-HPr complex (PDB: 1VRC) shows 48 kDa complex PMID:15788390

Localization

• Dual localization: found both membrane-associated and free in cytoplasm PMID:2999119
• Peripheral membrane protein associated with inner membrane PMID:16079137

Substrate specificity

• Primary substrates: mannose, glucose (2-deoxyglucose)
• Secondary substrates: fructose [PMID:4153999, PMID:4154035], N-acetylglucosamine PMID:6252281

Regulation

• manXYZ operon positively regulated by cAMP-CRP complex PMID:9484892
• Negatively regulated by Mlc transcriptional repressor PMID:9484892
• Weakly repressed by NagC PMID:11361067

Additional functions

• ManXYZ complex serves as chemoreceptor for sugar chemotaxis PMID:4604906
• ManXYZ required for phage lambda DNA injection, but ManY/ManZ alone sufficient [PMID:353494, PMID:2951378]

Review decisions

• Removed GO:0005515 (protein binding) - uninformative per curation guidelines
• Marked GO:0016301 (kinase activity) as over-annotated - too broad for PTS phosphotransferase
• Core MF: GO:0022870 (mannose PTS transporter activity)
• Secondary substrates (fructose, GlcNAc, glucose) kept as non-core