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33  structures 425  species 0  interactions 810  sequences 5  architectures

Family: LamB (PF02264)

Summary: LamB porin

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This is the Wikipedia entry entitled "Maltoporin". More...

Maltoporin Edit Wikipedia article

LamB porin
PDB 2mpr EBI.jpg
Structure of maltoporin from Salmonella typhimurium.[1]
Symbol LamB
Pfam PF02264
InterPro IPR003192
SCOP 2mpr
TCDB 1.B.3
OPM superfamily 32
OPM protein 2mpr
CDD cd01346

Maltoporins (or LamB porins) are a family of outer membrane proteins. Maltoporin forms a trimeric structure which facilitates the diffusion of maltodextrins across the outer membrane of Gram-negative bacteria. The membrane channel is formed by an antiparallel beta-barrel.[2] Maltoporin is a trimeric channel on the bacterial outer membrane. Most pores used for diffusion contain only 16 antiparallel strands, but Maltoporin has 18. The structure of Maltoporin contains long loops and short turns. The long loops are in contact with the cell exterior and the turns are in contact with the periplasm. This channel is involved in sugar transport. The sugar initially binds to the first greasy residue with van der Waals forces. The sugar continues through the channel by guided diffusion of the sugar along the greasy residues which form a "slide". Maltoporin's original name was LamB because it is a bacteriophage lambda receptor. This channel is specific because it has a binding site for maltosaccharides. The affinity of these maltosaccharides to the channel increases as the length of the chain increases.[3]


  1. ^ Meyer JE, Hofnung M, Schulz GE (March 1997). "Structure of maltoporin from Salmonella typhimurium ligated with a nitrophenyl-maltotrioside". J. Mol. Biol. 266 (4): 761–75. doi:10.1006/jmbi.1996.0823. PMID 9102468. 
  2. ^ Schirmer T, Rosenbusch JP, Keller TA, Wang YF (1995). "Structural basis for sugar translocation through maltoporin channels at 3.1 A resolution". Science. 267 (5197): 512–514. doi:10.1126/science.7824948. PMID 7824948. 
  3. ^ Ranquin,A. "Maltoporin: Sugar for physics and biology" Archived 2006-10-13 at the Wayback Machine., Elsevier,Retrieved on 27 April 2004.

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LamB porin Provide feedback

Maltoporin (LamB protein) forms a trimeric structure which facilitates the diffusion of maltodextrins across the outer membrane of Gram-negative bacteria. The membrane channel is formed by an antiparallel beta-barrel [1].

Literature references

  1. Schirmer T, Keller TA, Wang YF, Rosenbusch JP; , Science 1995;267:512-514.: Structural basis for sugar translocation through maltoporin channels at 3.1 A resolution [see comments] PUBMED:7824948 EPMC:7824948

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR003192

Maltoporin (LamB protein) forms a trimeric structure which facilitates the diffusion of maltodextrins across the outer membrane of Gram-negative bacteria. The membrane channel is formed by an antiparallel beta-barrel [ PUBMED:7824948 ]. Loop 3 folds into the core to constrict pore size. Long irregular loops are found on the extracelllular side, while short turns are in the periplasm. Tightly-bound water molecules are found in the eyelet of the passage, and only substrates that can displace and replace the broken hydrogen bonds are likely to enter the pore. Loops 4, 6, and 9 have the greatest mobility and are highly variable; these are postulated to attract maltodextrins [ PUBMED:9102468 ].

The porin LamB family also includes porin BglH, which may be a sugar porin with a broad carbohydrate specificity, and sucrose porin [ PUBMED:1649946 , PUBMED:9437428 ].

Gene Ontology

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Domain organisation

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Seed source: Pfam-B_4810 (release 5.2)
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Bateman A , Mian N
Number in seed: 62
Number in full: 810
Average length of the domain: 373.70 aa
Average identity of full alignment: 24 %
Average coverage of the sequence by the domain: 87.42 %

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HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 25.1 25.1
Trusted cut-off 25.9 25.7
Noise cut-off 24.7 24.5
Model length: 378
Family (HMM) version: 17
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Species distribution

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Archea Archea Eukaryota Eukaryota
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Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the LamB domain has been found. There are 33 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.

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