PT-TG is a conserved region found in many bacterial toxin proteins. It could function as a linker that links N-terminal secretion-related domain and C-terminal toxin domain. It contains a TG motif [].
Patatin-like phospholipase domain-containing protein 4 (PNPLA4), also known as GS2 (gene sequence-2) or iPLA2-eta (calcium-independent phospholipase A2), shows both lipase and transacylation activities []. GS2 lipase is expressed in various tissues, predominantly in muscle and adipocytes tissue. It is also expressed in keratinocytes and shows retinyl ester hydrolase, acylglycerol, TG hydrolase, and PLA2 activity [, , , , ].
This family represents PNPLA3 (patatin-like phospholipase domain-containing protein 3) from mammals, also known as ADPN (adiponutrin) or iPLA2-epsilon (calcium-independent phospholipase A2). PNPLA3 is a triacylglycerol lipase that mediates triacylglycerol hydrolysis in adipocytes and is an indicator of the nutritional state. Human adiponutrins are bound to the cell membrane of adipocytes and show transacylase, TG hydrolase, and PLA2 activity [, , ]. In murine models, PNPLA3 was found to be involved in the hepatic metabolism of triglycerides and in the regulation of systemic glucose homeostasis [].
This entry represents VSR (very short patch repair) endonucleases occurring in a variety of bacteria and some archaeal species, including DNA mismatch endonuclease Vsr from Escherichia coli. VSR recognises a TG mismatched base pair, generated after spontaneous deamination of methylated cytosines, and cleaves the phosphate backbone on the 5' side of the thymine []. GT mismatches can lead to C-to-T transition mutations if not repaired. VSR repairs the mismatches in favour of the G-containing strand. In Escherichia coli, this endonuclease nicks double-stranded DNA within the sequence CT(AT)GN or NT(AT)GG next to the thymidine residue, which is mismatched to 2'-deoxyguanosine []. The incision is mismatch-dependent and strand specific. The structure of VSR is similar to the core structure of restriction endonucleases, which have a 3-layer alpha/beta/alpha topology [].
Apolipoprotein C-III is a 79-residue glycoprotein synthesised in the intestine and liver as part of the very low density lipoprotein (VLDL) and the high density lipoprotein (HDL) particles. Owing to its positive correlation with plasma triglyceride (Tg) levels, Apo-CIII is suggested to play a role in Tg metabolism and is therefore of interest regarding atherosclerosis. However, unlike other apolipoproteins such as Apo-AI, Apo E or CII for which many naturally occurring mutations are known, the structure-function relationships of apo C-III remains a subject of debate. One possibility is that apo C-III inhibits lipoprotein lipase (LPL) activity, as shown by in vitroexperiments. Another suggestion, is that elevated levels of Apo-CIII displace other apolipoproteins at the lipoprotein surface, modifying their clearance from plasma [].
Apolipoprotein C-III is a 79-residue glycoprotein synthesised in the intestine and liver as part of the very low density lipoprotein (VLDL) and the high density lipoprotein (HDL) particles. Owing to its positive correlation with plasma triglyceride (Tg) levels, Apo-CIII is suggested to play a role in Tg metabolism and is therefore of interest regarding atherosclerosis. However, unlike other apolipoproteins such as Apo-AI, Apo E or CII for which many naturally occurring mutations are known, the structure-function relationships of apo C-III remains a subject of debate. One possibility is that apo C-III inhibits lipoprotein lipase (LPL) activity, as shown by in vitroexperiments. Another suggestion, is that elevated levels of Apo-CIII displace other apolipoproteins at the lipoprotein surface, modifying their clearance from plasma [].
Thyroglobulin (Tg) is a large glycoprotein specific to the thyroid gland and is the precursor of the iodinated thyroid hormones thyroxine (T4) and triiodothyronine (T3). The N-terminal section of Tg contains 10 repeats of a domain of about 65 amino acids which is known as the Tg type-1 repeat [, ]. Such a domain has also been found as a single or repeated sequence in the HLA class II associated invariant chain []; human pancreatic carcinoma marker proteins GA733-1 and GA733-2 []; nidogen (entactin), a sulphated glycoprotein which is widely distributed in basement membranes and that is tightly associated with laminin; insulin-like growth factor binding proteins (IGFBP) []; saxiphilin, a transferrin-like protein from Rana catesbeiana (Bull frog) that binds specifically to the neurotoxin saxitoxin []; chum salmon egg cysteine proteinase inhibitor, and equistatin, a thiol-protease inhibitor from Actinia equina (sea anemone) []. The existence of Thyr-1 domains in such a wide variety of proteins raises questions about their activity and function, and their interactions with neighbouring domains. The Thyr-1 and related domains belong to MEROPS proteinase inhibitor family I31, clan IX.Equistatin from A. equina is composed of three Thyr-1 domains; as with other proteins that contains Thyr-1 domains, the thyropins, they bind reversibly and tightly to cysteine proteases (inhibitor family C1). In equistatin inhibition of papain is a function of domain-1. Unusually domain-2 inhibits cathepsin D, an aspartic protease (inhibitor family A1) and has no activity against papain. Domain-3, does not inhibit either papain or cathepsin D, and its function or its target peptidase has yet to be determined [, ].
Thyroglobulin (Tg) is a large glycoprotein specific to the thyroid gland and is the precursor of the iodinated thyroid hormones thyroxine (T4) and triiodothyronine (T3). The N-terminal section of Tg contains 10 repeats of a domain of about 65 amino acids which is known as the Tg type-1 repeat [, ]. Such a domain has also been found as a single or repeated sequence in the HLA class II associated invariant chain []; human pancreatic carcinoma marker proteins GA733-1 and GA733-2 []; nidogen (entactin), a sulphated glycoprotein which is widely distributed in basement membranes and that is tightly associated with laminin; insulin-like growth factor binding proteins (IGFBP) []; saxiphilin, a transferrin-like protein from Rana catesbeiana (Bull frog) that binds specifically to the neurotoxin saxitoxin []; chum salmon egg cysteine proteinase inhibitor, and equistatin, a thiol-protease inhibitor from Actinia equina (sea anemone) []. The existence of Thyr-1 domains in such a wide variety of proteins raises questions about their activity and function, and their interactions with neighbouring domains. The Thyr-1 and related domains belong to MEROPS proteinase inhibitor family I31, clan IX.Equistatin from A. equina is composed of three Thyr-1 domains; as with other proteins that contains Thyr-1 domains, the thyropins, they bind reversibly and tightly to cysteine proteases (inhibitor family C1). In equistatin inhibition of papain is a function of domain-1. Unusually domain-2 inhibits cathepsin D, an aspartic protease (inhibitor family A1) and has no activity against papain. Domain-3, does not inhibit either papain or cathepsin D, and its function or its target peptidase has yet to be determined [, ].The thyroglobulin type-1 domain has an alpha+beta fold.
