double-psi beta-barrel fold of RlpA, N-terminal domain of expansins, and similar domains. The double-psi beta-barrel (DPBB) fold is found in a divergent group of proteins, including endolytic peptidoglycan transglycosylase RlpA (rare lipoprotein A), EG45-like domain containing proteins, kiwellins, Streptomyces papain inhibitor (SPI), and the N-terminal domain of plant and bacterial expansins. RlpA may work in tandem with amidases to degrade peptidoglycan (PG) in the division septum and lateral wall to facilitate daughter cell separation. An EG45-like domain containing protein from Arabidopsis thaliana, called plant natriuretic peptide A (AtPNP-A), functions in cell volume regulation. Kiwellin proteins comprise a widespread family of plant-defense proteins that target pathogenic bacterial/fungal effectors that down-regulate plant defense responses. SPI is a stress protein produced under hyperthermal stress conditions that serves as a glutamine and lysine donor substrate for microbial transglutaminase (MTG, EC 2.3.2.13) from Streptomycetes. Some expansin family proteins display cell wall loosening activity and are involved in cell expansion and other developmental events during which cell wall modification occurs.
N-terminal double-psi beta-barrel fold domain of the expansin family and similar domains. The plant expansin family consists of four subfamilies, alpha-expansin (EXPA), beta-expansin (EXPB), expansin-like A (EXLA), and expansin-like B (EXLB). EXPA and EXPB display cell wall loosening activity and are involved in cell expansion and other developmental events during which cell wall modification occurs. EXPA proteins function more efficiently on dicotyledonous cell walls, whereas EXPB proteins exhibit specificity for the cell walls of monocotyledons. Expansins also affect environmental stress responses. Expansin family proteins contain an N-terminal domain (D1) homologous to the catalytic domain of glycoside hydrolase family 45 (GH45) proteins but with no hydrolytic activity, and a C-terminal domain (D2) homologous to group-2 grass pollen allergens. This family also includes GH45 endoglucanases from mollusks. This model represents the N-terminal domain of expansins and similar proteins, which adopts a double-psi beta-barrel (DPBB) fold.
double-psi beta-barrel fold of Streptomyces papain inhibitor and similar proteins. Streptomyces papain inhibitor (SPI) adopts a rigid, thermo-resistant double-psi-beta-barrel (DPBB) fold that is stabilized by two cysteine bridges. SPI serves as a glutamine and lysine donor substrate for microbial transglutaminase (MTG, EC 2.3.2.13) from Streptomycetes, that is used to covalently and specifically link functional amines to glutamine donor sites of therapeutic proteins. SPI is a stress protein produced under hyperthermal stress conditions, and is able to inhibit the cysteine proteases, papain and bromelain, as well as the bovine serine protease trypsin.
double-psi beta-barrel fold of EG45-like domain-containing proteins. This family contains plant EG45-like domain-containing proteins which show sequence similarity to expansins, and similar proteins. Citrus jambhiri EG45-like domain-containing protein was identified as a protein associated with citrus blight (CB), and is also called blight-associated protein p12 (CjBAp12) or plant natriuretic peptide (PNP). CjBAp12 does not display cell wall loosening activity of expansins. Arabidopsis thaliana EG45-like domain-containing protein 2, also called plant natriuretic peptide A (AtPNP-A), is a systemically mobile natriuretic peptide immunoanalog, recognized by antibodies against vertebrate atrial natriuretic peptides (ANPs), that functions in cell volume regulation. Thus, it has an important and systemic role in plant growth and homeostasis. Due to their similarity to the N-terminal domain of expansin and to endolytic peptidoglycan transglycosylase RlpA, EG45-like domain-containing proteins may adopt a double-psi beta-barrel fold.