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Structure of Cyanothece McdB
Structural highlights
FunctionMCDB_GLOC7 McdA and McdB together mediate carboxysome (Cb) spacing, size, ultrastucture and probably inheritance in the cell, together they prevent Cb aggregation. McdA is an ATPase that forms dynamic gradients on the nucleoid in response to adapter protein McdB, which associates with carboxysomes. The interplay between McdA gradients on the nucleoid and McdB-bound carboxysomes result in the equal spacing of Cbs along the cell length. Stimulates the ATPase activity of McdA, causing McdA to be released from DNA. Undergoes liquid-liquid phase separation.[UniProtKB:Q8GJM6] Incorrect positioning (aggregation) of carboxysomes results in reduced CO(2) fixation by encapsulated ribulose-1,5-bisphosphate carboxylase (RuBisCO, cbbL/cbbS), which leads to slower growth.[UniProtKB:Q8GJM6] Publication Abstract from PubMedCarboxysomes, protein-coated organelles in cyanobacteria, are important in global carbon fixation. However, these organelles are present at low copy in each cell and hence must be segregated to ensure transmission from one generation to the next. Recent studies revealed that a DNA partition-like ParA-ParB system mediates carboxysome maintenance, called McdA-McdB. Here, we describe the first McdA and McdB homolog structures. McdA is similar to partition ParA Walker-box proteins, but lacks the P-loop signature lysine involved in ATP binding. Strikingly, a McdA-ATP structure shows that a lysine distant from the P-loop and conserved in McdA homologs, enables ATP-dependent nucleotide sandwich dimer formation. Similar to partition ParA proteins this ATP-bound form binds nonspecific-DNA. McdB, which we show directly binds McdA, harbors a unique fold and appears to form higher-order oligomers like partition ParB proteins. Thus, our data reveal a new signature motif that enables McdA dimer formation and indicates that, similar to DNA segregation, carboxysome maintenance systems employ Walker-box proteins as DNA-binding motors while McdB proteins form higher order oligomers, which could function as adaptors to link carboxysomes and provide for stable transport by the McdA proteins. Structures of maintenance of carboxysome distribution Walker-box McdA and McdB adaptor homologs.,Schumacher MA, Henderson M, Zhang H Nucleic Acids Res. 2019 May 20. pii: 5491742. doi: 10.1093/nar/gkz314. PMID:31106331[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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