1.B.15 The Raffinose Porin (RafY) Family

The RafY family consists of a single porin protein, RafY, encoded within the E. coli plasmid pRSD2. pRSD2 also encodes the permease and enzymes required for raffinose utilization. The gene order is: rafR (regulatory protein), rafA (α-galactosidase), rafB (permease), rafD (invertase) and rafY (porin). The RafY porin in the outer membrane of E. coli can accommodate many oligosaccharides including several disaccharides, the trisaccharide raffinose, the tetrasaccharides maltotetraose and stachyose, the hexasaccharide maltohexaose and the heptasaccharide maltoheptaose. Thus, RafY is a general porin capable of transporting many oligosaccharides and other molecules across the outer membrane of Gram-negative bacteria. In this respect it resembles ScrY (TC #1.B.3.1.2), the sucrose porin, which also exhibits broad specificity, but not MalL (LamB) (TC #1.B.3.1.1), maltoporin which is largely specific for maltooligosaccharides. However, it has been shown to transport ions with slight selectivity for cations over anions. It appears to have a relatively large inner pore diameter and to lack a carbohydrate binding site.

The generalized transport reaction catalyzed by RafY is:

Solute (out) Solute (periplasm).



This family belongs to the Outer Membrane Pore-forming Protein (OMPP) Superfamily I.

 

References:

Andersen, C., D. Krones, C. Ulmke, K. Schmid and R. Benz (1998). The porin RafY encoded by the raffinose plasmid pRSD2 of Escherichia coli forms a general diffusion pore and not a carbohydrate-specific porin. Eur. J. Biochem. 254: 679-684.

Ulmke, C., J.W. Lengeler and K. Schmid (1997). Identification of a new porin, RafY, encoded by raffinose plasmid pRSD2 of Escherichia coli. J. Bacteriol. 179: 5783-5788.

Examples:

TC#NameOrganismal TypeExample
1.B.15.1.1Raffinose porin, RafY Gram-negative bacteria RafY of E. coli
 
1.B.15.1.2

Putative glycoporin

γ-Proteobacteria

Putative porin of Vibrio shilonii

 
1.B.15.1.3

Putative porin

β-Proteobacteria

Putative porin of Polaromonas naphthalenivorans

 
1.B.15.1.4

Putative porin of 374 aas

Proteobacteria

Putative porin of Vibrio harveyi

 
1.B.15.1.5

Putative porin

Proteobacteria

Putative porin of Pychromonas ingrahamii

 
Examples:

TC#NameOrganismal TypeExample