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2.A.2.1.1
Melibiose permease. Catalyzes the coupled stoichiometric symport of a galactoside with a cation (either Na+, Li+, or H+). Based on LacY, a 3-d model has been derived (Yousef and Guan, 2009). Asp55 and Asp59 are essential for Na+ binding. Asp124 may play a critical role by allowing Na+-induced conformational changes and sugar binding. Asp19 may facilitate melibiose binding (Granell et al., 2010).  The alternate access mechanism fits better into a flexible gating mechanism rather than the archetypical helical rigid- body rocker-switch mechanism (Wang et al. 2016).  Crystal structures of Salmonella typhimurium MelB in two conformations, representing an outward partially occluded and an outward inactive state (Ethayathulla et al. 2014). MelB adopts a typical MFS fold and contains a previously unidentified cation-binding motif. Three conserved acidic residues form a pyramidal-shaped cation-binding site for Na+, Li+ or H+, which is in close proximity to the sugar-binding site. Both cosubstrate-binding sites are mainly contributed by the residues from the amino-terminal domain (Ethayathulla et al. 2014). The Glucose Enzyme IIA protein of the PTS binds MelB either in the absence or presence of a galactoside, and binding decreases the affinity for melibiose, giving rise to inducer exclusion (Saier 1989; Hariharan and Guan 2014).

Accession Number:A7ZUZ0
Protein Name:Melibiose carrier protein
Length:473
Molecular Weight:52624.00
Species:Escherichia coli O139:H28 (strain E24377A / ETEC) [331111]
Number of TMSs:11
Location1 / Topology2 / Orientation3: Cell inner membrane1 / Multi-pass membrane protein2
Substrate Melibiose

Cross database links:

eggNOG: COG2211
HEGENOM: HBG467489
RefSeq: YP_001465619.1   
Entrez Gene ID: 5589204   
KEGG: ecw:EcE24377A_4   

Gene Ontology

GO:0016020 C:membrane
GO:0005215 F:transporter activity
GO:0006814 P:sodium ion transport

References (1)

[1] “The pangenome structure of Escherichia coli: comparative genomic analysis of E. coli commensal and pathogenic isolates.”  Rasko D.A.et.al.   18676672

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FASTA formatted sequence
1:	MSISMTTKLS YGFGAFGKDF AIGIVYMYLM YYYTDVVGLS VGLVGTLFLV ARIWDAINDP 
61:	IMGWIVNATR SRWGKFKPWI LIGTLANSVI LFLLFSAHLF EGTTQIVFVC VTYILWGMTY 
121:	TIMDIPFWSL VPTITLDKRE REQLVPYPRF FASLAGFVTA GVTLPFVNYV GGGDRGFGFQ 
181:	MFTLVLIAFF IVSTIITLRN VHEVFSSDNQ PSAEGSHLTL KAIVALIYKN DQLSCLLGMA 
241:	LAYNVASNII TGFAIYYFSY VIGDADLFPY YLSYAGAANL VTLVFFPRLV KSLSRRILWA 
301:	GASILPVLSC GVLLLMALMS YHNVVLIVIA GILLNVGTAL FWVLQVIMVA DTVDYGEYKL 
361:	HVRCESIAYS VQTMVVKGGS AFAAFFIAVV LGMIGYVPNV EQSTQALLGM QFIMIALPTL 
421:	FFMVTLILYF RFYRLNGDTL RRIQIHLLDK YRKVPPEPVH ADIPVGAVSD VKA