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3.A.1.122.35
The MacAB drug exporter.  MacB is an ABC transporter that collaborates with the MacA adaptor protein (a membrane fusion protein, MFP) and the TolC exit duct to drive efflux of antibiotics and enterotoxin STII out of the bacterial cell. Crow et al. 2017 presented the structure of ATP-bound MacB and reveal precise molecular details of its mechanism. The MacB transmembrane domain lacks a central cavity through which substrates could be passed, but instead conveys conformational changes from one side of the membrane to the other, a process termed mechanotransmission. Comparison of ATP-bound and nucleotide-free states revealed how reversible dimerization of the nucleotide binding domains drives opening and closing of the MacB periplasmic domains via concerted movements of the second transmembrane segment and the major coupling helix. They proposed that the assembled tripartite pump acts as a molecular bellows to propel substrates through the TolC exit duct, driven by MacB mechanotransmission. Homologs of MacB that do not form tripartite pumps, but share structural features underpinning mechanotransmission, include the LolCDE lipoprotein trafficking complex and FtsEX cell division signaling protein. The MacB architecture serves as a blueprint for understanding the structure and mechanism of an entire ABC transporter superfamily and the many diverse functions it supports (Crow et al. 2017). The crystal structure of MacA has been solved (Yum et al. 2009).

Accession Number:Q2EHL8
Protein Name:Macrolide export ATP-binding/permease protein MacB
Length:644
Molecular Weight:69871.00
Species:Aggregatibacter actinomycetemcomitans (Actinobacillus actinomycetemcomitans) [714]
Number of TMSs:5
Location1 / Topology2 / Orientation3: Cell inner membrane1 / Multi-pass membrane protein2
Substrate

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FASTA formatted sequence
1:	MNIIEIKQLN RYFGEGENRV HVLKDISLSI ERGDFVAIMG QSGSGKSTLM NIIGCLDTAT 
61:	GGSSKIDGKE TIELTNDQLS DLRSQKFGFI FQRYNLLSSL TAAENVALPA IYAGMPQSQR 
121:	LERAKQLLEK LGLGDKWQNK PNQLSGGQQQ RVSIARALMN GGEIILADEP TGALDSHSGE 
181:	NVMEILRQLH EEGHTIIMVT HDKHIAASAN RIIEIKDGEI ISDTQKRQVK SAVKNPSVFK 
241:	GRFGFSKDQL MEAFRMSVSA IVAHKMRSLL TMLGIIIGIT SVVSVVALGN GSQQKILENI 
301:	RGIGTNTMTI FNGNGFGDRR SRHIQNLKIS DANTLSKQSY IQSVTPNTSS SGILVVGNKS 
361:	FTSANLYGIG EQYFDVEGLK LKQGRLLTED DVDQSNQVVV LDESAKKAIF ANENPLGKTV 
421:	IFNKRPFRVI GVVSDQQLGG FPGNSLNLYS PYSTVLNKIT GGSRIGSITV KISDDVNSTV 
481:	AEKSLTELLK SLHGKKDFFI MNSDTIKQTI ENTTGTMKLL ISSIAFISLI VGGIGVMNIM 
541:	LVSVTERTKE IGVRMAIGAR QINILQQFLI EAVLICLIGG VAGILLSVLI GVLFNSFITD 
601:	FSMDFSTASI VTAVLFSTLI GVLFGYMPAK KAAELNPITA LAQE