Phosphate permeases are membrane transport proteins that facilitate the diffusion of phosphate into and out of a cell or organelle. Some of these families include:
The Pho1 phosphate permease family is a family of phosphate transporters belonging to the ion transporter (IT) superfamily. Representative members of the Pho1 family include the putative phosphate transporter PHO1 of Arabidopsis thaliana, and the xenotropic and polytropic murine-leukemia virus receptor Xpr1 of Culex pipiens.
The Deinococcus/Thermus Holin (D/T-Hol) Family consists of a single protein with no close homologues ; however, its distant homology to members of the Holin superfamily III suggest an evolutionary relationship. The putative holin of Meiothermus silvanus is 108 amino acyl residues in length and possesses 3 transmembrane segments.
The Pseudomonas aeruginosa Hol Holin Family is a group of transporters belonging to the Holin Superfamily III.
The Holin superfamily V is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total. In general, these proteins are thought to play a role in regulated cell death, although functionality varies between families and individual members. The Holin superfamily V includes the TC families:
The Holin superfamily VII is a superfamily of integral membrane transport proteins. It is one of the seven different holin superfamilies in total. In general, these proteins are thought to play a role in regulated cell death, although functionality varies between families and individual members.
The Listeria Phage A118 Holin (Hol118) Family is a group of transporters belonging to the Holin Superfamily V. A representative list of proteins belonging to the Hol118 family can be found in the Transporter Classification Database.
The putative holin-like toxin (Hol-Tox) family consists of many small proteins, between 34 and 48 amino acyl residues (aas) with a single transmembrane segment (TMSs). Rajesh et al. first identified the gene and designated it tmp1, which coded for a 34 amino acyl peptide that acts as an antibacterial agent on gram-positive bacteria. This peptide exhibits a single transmembrane domain (TMD) that is believed to play a role in facilitating the antibacterial activity. A representative list of proteins belonging to the Hol-Tox family can be found in the Transporter Classification Database.
The Putative 3-4 TMS Transglycosylase-associated Holin Family is believed to be a group of holins that does not belong to one of the seven holin superfamilies. Homologues include thousands of diverse phage and bacterial proteins between 80 and 140 amino acyl residues (aas) in length that exhibit 3 to 4 transmembrane segments (TMSs). These proteins are holin-like in their size and topology and are designated 'Transglycosylase-associated', 'Putative holin', 'Phage-like transmembrane protein', 'YeaQ protein', etc. in the NCBI protein database. As of early 2016, they remain functionally uncharacterized. They derive from a wide range of bacterial and archaeal phyla including both Gram-negative and Gram-positive bacteria. These proteins are related to the RDD family in the conserved domain database. A representative list of proteins belonging to the T-A Hol family can be found in the Transporter Classification Database.
The CaulobacterPhage Holin (CauHol) Family consists of several putative holins of 157 to 159 amino acyl residues (aas) in length that exhibit 2 transmembrane segments (TMSs). They derive from phage specific for Caulobacter species. These proteins are not functionally characterized. A representative list of proteins belonging to the CauHol family can be found in the Transporter Classification Database.
The Putative Listeria Phage Holin (LP-Hol) Family consists of several small proteins of 41 amino acyl residues (aas) and 1 transmembrane segment (TMS). They can be found in several Listeria phage as well as in Listeria monocytogenes. While annotated as holins, these proteins remain functionally uncharacterized. A representative list of proteins belonging to the LP-Hol family can be found in the Transporter Classification Database.
The Flp/Fap Pilin Putative Holin (FFPP-Hol) Family is a large diverse family with members from many bacterial phyla. Some members are annotated as Flp or Fap pilin subunits; others are identified as Holin BlyA family members. They range in size of 50 to 80 amino acyl residues (aas) with a single N-terminal transmembrane segment (TMS) although one member has 99 aas and 2 TMSs. Flp homologues are included in TCDB under TC# 3.A.7.13.1 (pXO1-63) and TC# 3.A.7.15.1 (Flp-1). As on March 2016, their precise functions appear to be unknown. A representative list of proteins belonging to the FFPP-Hol family can be found in the Transporter Classification Database.
The Putative 3 TMS Holin (3-Hol) Family is large, consisting of many members derived from proteobacteria and their phage, all of small size and usually with 3 transmembrane segments (TMSs). A representative list of the proteins belonging to this family can be found in the Transporter Classification Database. While many of the proteins belonging to this family are annotated in holins, they remain functionally uncharacterized.
The Actinobacterial Phage Holin (APH) Family is a fairly large family of proteins between 105 and 180 amino acyl residues in length, typically exhibiting a single transmembrane segment (TMS) near the N-terminus. A representative list of proteins belonging to the APH family can be found in the Transporter Classification Database.
The Prophage Hp1 Hol (Hp1Hol) Family consists of a single putative holin of 69 amino acyl residues in length, exhibiting what appears to be a single transmembrane segment (TMS). It is derived from the firmicute, Clostridium hathewayi DSM 13479. This protein is functionally uncharacterized and does not appear to be homologous to other holins. It does, however, show 31% identity to a heavy metal transporter from Dethiosulfovibrio peptidovorans.
The Putative Archaeal 2 TMS Holin (A2-Hol) Family consists of a few putative holins from Thaumarchaeota ranging in size from about 130 to 165 amino acyl residues (aas) and exhibiting 2 transmembrane segments (TMSs). A representative list of proteins belonging to the A2-Hol family can be found in the Transporter Classification Database. The archaeon, Candidatus Nitrosoarchaeum limnia, encodes adjacent genes designated Toxin Secretion/Lysis Holin. The "toxin" gene encodes a soluble protein of 325 aas stated as belonging to the "Glycosyltransferase GBT-type Superfamily". This protein brings up other glycosyltransferases in a NCBI BLAST search. The adjacent gene encodes a small protein of 132 aas and 2 TMSs that could be a holin, based on its size and topology. This protein has the UniProt accession number of S2E3C4. Paralogues are found in this same organism and other closely related species.
The Putative Bacterial Archaeal Holin(BAH) Family consists of several uncharacterized proteins. However, these proteins were retrieved when functionally characterized holins from the T-A Hol family were BLASTED against the NCBI database, and thus may be related to the T-A Hol family. Most BAH proteins are between 125 and 140 amino acyl residues (aas) in length and exhibit 4 transmembrane segments (TMSs), although at least one putative holin is almost 260 aas long. A representative list of proteins belonging to the BAH family can be found in the Transporter Classification Database.
The Malonate:Na+ Symporter (MSS) Family (TC# 2.A.70) is a group of transport proteins belonging to the CPA superfamily. These proteins are composites with constituents ranging in size from 129 to 255 amino acyl residues (aas) and exhibiting 4 to 7 transmembrane segments (TMSs). A representative list of proteins belonging to the MSS family can be found in the Transporter Classification Database.
