2.A.122 The LrgB/CidB Holin-like Glycolate/Glycerate Transporter (LrgB/CidB/GGT) Family
CidA and LrgA are a putative holin/antiholin pair in Staphylococcus aureus. LrgB is LrgA-associated (lrgA and lrgB are translationally coupled) while CidB is CidA-associated (cidA and cidB are similarly translationally coupled). Both have been reported to play a role in cell wall hydrolysis, possibly by regulating murein hydrolase export. The cidABC operon is controlled by CidR, encoded adjacent to the cidABC operon, and the lrgABC operon is controlled by LrgR, encoded upstream of the lrgABC operon. Cell lysis results in response to acetic acid accumulation in the medium (Yang et al. 2005).
A longer homologue of the bacterial LrgB has been shown to be the plastidic glycolate glycerate transporter, PLGG1, of 512 aas and 12 TMSs in Arabidopsis thaliana (Pick et al. 2013). The last 5 TMSs are homologous to the 5 TMSs in several CidB and LrgB proteins of bacteria (see proteins 2.A.122.1.1 and 1.2). This plant protein may represent a fusion of the bacterial LrgA and LrgB proteins (Wang and Bayles 2013). Because of this function, it appears that at least this plant protein of 12 TMSs must be a secondary carrier.
LrgB (YohK) protein (putative murein hydrolase export regulator; LrgA-associated protein) (7 probable TMSs based on topological analyses. This protein and 2.A.122.1.2 with 8 TMSs appear to derive from a 4 TMS precursor that duplicated to give 8, and LrgB may have lost TMS 1. It does not appear to be a member of the TOG superfamily.). LrgB decreases antibiotic sensitivity (Yang et al., 2005).
LrgB of E. coli (C6EAH0)
Putative holin-mediated export regulatory protein, CidB (8 TMSs with an internal repeat of 4 TMSs). It enhances antibiotic sensitivity (Yang et al., 2005). CidA is a holin-like protein (TC# 1.E.14.1.2). The cidABC operon is controlled by CidR, an activator in the presence of acetic acid (Yang et al., 2005).
CidB of Staphylococcus aureus (H4HJS5)
Putative antiholin-like protein of 233 aas and 8 TMSs, LrgB (Chu et al. 2013). Proposed to function together with LrgA as a holin/antiholin pair to export autolysins, LytM and LytN. However, the identification of a larger fused plant homologue (9.B.117.1.4) as a plastidic glycolate glycerate transporter (Pick et al. 2013) sheds doubt on this proposal.
LrgB of Staphylococcus aureus
Putative murein hydrolase export regulator LrgB of 231 aas and 8 putative TMSs (Ahn et al. 2010).
Putative murein hydrolase export regulator, LrgB, of Streptococcus mutans
Putative antiholin of 225 aas and 6 TMSs, LrgB or YwbG (Chen et al. 2015). Inhibits the activity of putative holin, CidA or YwbH (TC# 1.E.14.1.16).
YwbG of Bacillus subtilis
Putative antiholin of 231 aas and 8 TMSs, YsbB or LrgB (Chen et al. 2015). Believed to counteract the holin activity of YsbA (TC# 1.E.14.1.17).
YsbB of Bacillus subtilis
Putative anit-holin, YxaC of 230 aas and 6-8 TMSs (Chen et al. 2015).
YxaC of Bacillus subtilis
Plastidic glycolate glycerate transporter, PLGG1, of 512 aas and 12 TMSs (Pick et al. 2013). The last TMSs are homologous to the TMSs in several CidB and LrgB proteins of bacteria. This plant protein may represent a fusion of the bacterial LrgA and LrgB proteins (Yang et al. 2012; Wang and Bayles 2013). Rice OsPLGG1 is the ortholgous plastidic glycolate/glycerate transporter, which is necessary for photorespiration and growth in rice (Shim et al. 2019).
PLGG1 of Arabidopsis thaliana
LrgB1 of 519 aas and 15 putative TMSs.
LrgB1 of Oryza sativa
LrgB2 of 458 aas and 12 - 14 TMSs.
LrgB2 of Oryza sativa
LrgB of 455 aas (Wang and Bayles 2013).
LrgB of Chlamydomonas reinhardtii (Chlamydomonas smithii)
LrgB1 of 455 aas (Wang and Bayles 2013).
LrgB1 of Thalassiosira pseudonana (Marine diatom) (Cyclotella nana)
LrgB2 of 413 aas (Wang and Bayles 2013).
LrgB2 of Thalassiosira pseudonana (Marine diatom) (Cyclotella nana)
Uncharacterized protein of 604 aas and 11 TMSs.
UP of Trichoderma harzianum