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3.A.1.1.1
Maltooligosaccharide porter. The 3-D structure has been reported by Oldham et al. (2007). An altering access mechanism has been suggested for the maltose transporter resulting from rigid-body rotations (Khare et al., 2009). The maltose-binding protein is open in the catalytic transition state for ATP hydrolysis during maltose transport (Austermuhle et al. 2004). Bordignon et al. (2010) and Schneider et al. (2012) reviewed the extensive knowledge available on MalEFGK2, its mode of action and its regulatory interactions.  The transporter sequesters the MalT transcriptional activator at the cytoplasmic surface of the membrane in the absence of the transport substrate (Richet et al. 2012).  The crystal structures of the transporter complex MBP-MalFGK2 bound with large malto-oligosaccharide in two different conformational states have also been determined. In the pretranslocation structure, Oldham et al. 2013 found that the transmembrane subunit MalG forms two hydrogen bonds with malto-oligosaccharide at the reducing end. In the outward-facing conformation, the transmrembrane subunit MalF binds three glucosyl units from the nonreducing end. These structural features explain why large modified malto-oligosaccharides are not transported by MalFGK2 despite their high binding affinity to MBP. In the transport cycle, substrate is channeled from MBP into the transmembrane pathway with a polarity such that both MBP and MalFGK2 contribute to the overall substrate selectivity of the system (Oldham et al. 2013).  Stabilization of the semi-open MalK2 conformation by maltose-bound MBP is key to the coupling of maltose transport to ATP hydrolysis in vivo, because it facilitates the progression of the MalK dimer from the open to the semi-open conformation, from which it can proceed to hydrolyze ATP (Alvarez et al. 2015). Both the binding of MalE to the periplasmic side of the transmembrane complex and binding of ATP to MalK2 are necessary to facilitate the conformational change from the inward-facing state to the occluded state, in which MalK2 is completely dimerized (Hsu et al. 2017). An integrated transport mechanism of the maltose ABC importer has been proposed (Mächtel et al. 2019).

Accession Number:P68183
Protein Name:Maltose transport system permease protein MalG aka B4032
Length:296
Molecular Weight:32225.00
Species:Escherichia coli [83333]
Number of TMSs:6
Location1 / Topology2 / Orientation3: Cell inner membrane1 / Multi-pass membrane protein2
Substrate Maltooligosaccharides, Maltose

Cross database links:

RefSeq: AP_004533.1    NP_418456.1   
Entrez Gene ID: 948530   
Pfam: PF00528   
BioCyc: EcoCyc:MALG-MONOMER    ECOL168927:B4032-MONOMER   
KEGG: ecj:JW3992    eco:b4032   

Gene Ontology

GO:0043190 C:ATP-binding cassette (ABC) transporter complex
GO:0016021 C:integral to membrane
GO:0005886 C:plasma membrane
GO:0015609 F:maltooligosaccharide-importing ATPase activity
GO:0015423 F:maltose-transporting ATPase activity
GO:0042956 P:maltodextrin transport
GO:0015768 P:maltose transport

References (13)

[1] “Sequence of gene malG in E. coli K12: homologies between integral membrane components from binding protein-dependent transport systems.”  Dassa E.et.al.   3000770
[2] “Analysis of the Escherichia coli genome. IV. DNA sequence of the region from 89.2 to 92.8 minutes.”  Blattner F.R.et.al.   8265357
[3] “The complete genome sequence of Escherichia coli K-12.”  Blattner F.R.et.al.   9278503
[4] “Highly accurate genome sequences of Escherichia coli K-12 strains MG1655 and W3110.”  Hayashi K.et.al.   16738553
[5] “The cloning and DNA sequence of the gene xylE for xylose-proton symport in Escherichia coli K12.”  Davis E.O.et.al.   2820984
[6] “3' end of the malEFG operon in E.coli: localization of the transcription termination site.”  Francoz E.et.al.   2836810
[7] “Cellular localization of the MalG protein from the maltose transport system in Escherichia coli K12.”  Dassa E.et.al.   2233678
[8] “Membrane topology of MalG, an inner membrane protein from the maltose transport system of Escherichia coli.”  Dassa E.et.al.   8437518
[9] “Sequence-function relationships in MalG, an inner membrane protein from the maltose transport system in Escherichia coli.”  Dassa E.et.al.   8437519
[10] “Subunit interactions in ABC transporters: a conserved sequence in hydrophobic membrane proteins of periplasmic permeases defines an important site of interaction with the ATPase subunits.”  Mourez M.et.al.   9214624
[11] “ATP modulates subunit-subunit interactions in an ATP-binding cassette transporter (MalFGK2) determined by site-directed chemical cross-linking.”  Hunke S.et.al.   10809785
[12] “Maltose/maltodextrin system of Escherichia coli: transport, metabolism, and regulation.”  Boos W.et.al.   9529892
[13] “Global topology analysis of the Escherichia coli inner membrane proteome.”  Daley D.O.et.al.   15919996
Structure:
2R6G   3FH6   3PUV   3PUW   3PUX   3PUY   3PUZ   3PV0   3RLF   4JBW   [...more]

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FASTA formatted sequence
1:	MAMVQPKSQK ARLFITHLLL LLFIAAIMFP LLMVVAISLR QGNFATGSLI PEQISWDHWK 
61:	LALGFSVEQA DGRITPPPFP VLLWLWNSVK VAGISAIGIV ALSTTCAYAF ARMRFPGKAT 
121:	LLKGMLIFQM FPAVLSLVAL YALFDRLGEY IPFIGLNTHG GVIFAYLGGI ALHVWTIKGY 
181:	FETIDSSLEE AAALDGATPW QAFRLVLLPL SVPILAVVFI LSFIAAITEV PVASLLLRDV 
241:	NSYTLAVGMQ QYLNPQNYLW GDFAAAAVMS ALPITIVFLL AQRWLVNGLT AGGVKG