P-loop containing Nucleoside Triphosphate Hydrolases; Members of the P-loop NTPase domain superfamily are characterized by a conserved nucleotide phosphate-binding motif, also referred to as the Walker A motif (GxxxxGK[S/T], where x is any residue), and the Walker B motif (hhhh[D/E], where h is a hydrophobic residue). The Walker A and B motifs bind the beta-gamma phosphate moiety of the bound nucleotide (typically ATP or GTP) and the Mg2+ cation, respectively. The P-loop NTPases are involved in diverse cellular functions, and they can be divided into two major structural classes: the KG (kinase-GTPase) class which includes Ras-like GTPases and its circularly permutated YlqF-like; and the ASCE (additional strand catalytic E) class which includes ATPase Binding Cassette (ABC), DExD/H-like helicases, 4Fe-4S iron sulfur cluster binding proteins of NifH family, RecA-like F1-ATPases, and ATPases Associated with a wide variety of Activities (AAA). Also included are a diverse set of nucleotide/nucleoside kinase families.

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                  ....*....|....*....|....*....|....*....|....*....|....
gi 2462598888 346 KIEKLLAMGDLSSSTPWHLQPTCAIIGDGLKEGLEKLHDMIIKRRKMLRQQKKK 399
Cdd:cd04152   129 EVEKLLALHELSSSTPWHVQPACAIIGEGLQEGLEKLYEMILKRRKMLRQQKKK 182

Arf-like 4 (Arl4) and 7 (Arl7) GTPases; Arl4 (Arf-like 4) is highly expressed in testicular germ cells, and is found in the nucleus and nucleolus. In mice, Arl4 is developmentally expressed during embryogenesis, and a role in somite formation and central nervous system differentiation has been proposed. Arl7 has been identified as the only Arf/Arl protein to be induced by agonists of liver X-receptor and retinoid X-receptor and by cholesterol loading in human macrophages. Arl7 is proposed to play a role in transport between a perinuclear compartment and the plasma membrane, apparently linked to the ABCA1-mediated cholesterol secretion pathway. Older literature suggests that Arl6 is a part of the Arl4/Arl7 subfamily, but analyses based on more recent sequence data place Arl6 in its own subfamily.

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                  ....*....|....*....|....*....|....*....|....*....|....
gi 2462598888 346 KIEKLLAMGDLSSSTPWHLQPTCAIIGDGLKEGLEKLHDMIIKRRKMLRQQKKK 399
Cdd:cd04152   129 EVEKLLALHELSSSTPWHVQPACAIIGEGLQEGLEKLYEMILKRRKMLRQQKKK 182

ARF-like small GTPases; ARF, ADP-ribosylation factor; Ras homologues involved in vesicular transport. Activator of phospholipase D isoforms. Unlike Ras proteins they lack cysteine residues at their C-termini and therefore are unlikely to be prenylated. ARFs are N-terminally myristoylated. Contains ATP/GTP-binding motif (P-loop).

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                   ....*....|....*....|..
gi 2462598888  361 PWHLQPTCAIIGDGLKEGLEKL 382
Cdd:smart00177 148 NWYIQPTCATSGDGLYEGLTWL 169

Arf-like 4 (Arl4) and 7 (Arl7) GTPases; Arl4 (Arf-like 4) is highly expressed in testicular germ cells, and is found in the nucleus and nucleolus. In mice, Arl4 is developmentally expressed during embryogenesis, and a role in somite formation and central nervous system differentiation has been proposed. Arl7 has been identified as the only Arf/Arl protein to be induced by agonists of liver X-receptor and retinoid X-receptor and by cholesterol loading in human macrophages. Arl7 is proposed to play a role in transport between a perinuclear compartment and the plasma membrane, apparently linked to the ABCA1-mediated cholesterol secretion pathway. Older literature suggests that Arl6 is a part of the Arl4/Arl7 subfamily, but analyses based on more recent sequence data place Arl6 in its own subfamily.

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                  ....*....|....*....|....*....|....*....|....*....|....
gi 2462598888 346 KIEKLLAMGDLSSSTPWHLQPTCAIIGDGLKEGLEKLHDMIIKRRKMLRQQKKK 399
Cdd:cd04152   129 EVEKLLALHELSSSTPWHVQPACAIIGEGLQEGLEKLYEMILKRRKMLRQQKKK 182

ADP-ribosylation factor(Arf)/Arf-like (Arl) small GTPases; Arf (ADP-ribosylation factor)/Arl (Arf-like) small GTPases. Arf proteins are activators of phospholipase D isoforms. Unlike Ras proteins they lack cysteine residues at their C-termini and therefore are unlikely to be prenylated. Arfs are N-terminally myristoylated. Members of the Arf family are regulators of vesicle formation in intracellular traffic that interact reversibly with membranes of the secretory and endocytic compartments in a GTP-dependent manner. They depart from other small GTP-binding proteins by a unique structural device, interswitch toggle, that implements front-back communication from N-terminus to the nucleotide binding site. Arf-like (Arl) proteins are close relatives of the Arf, but only Arl1 has been shown to function in membrane traffic like the Arf proteins. Arl2 has an unrelated function in the folding of native tubulin, and Arl4 may function in the nucleus. Most other Arf family proteins are so far relatively poorly characterized. Thus, despite their significant sequence homologies, Arf family proteins may regulate unrelated functions.

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                  ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 2462598888 331 KDPDLKTLFTKIGCKKIEKLLAMG--DLSS--------STPWHLQPTCAIIGDGLKEGLEKL 382
Cdd:cd00878    94 NEEELKGAPLLILANKQDLPGALTesELIEllglesikGRRWHIQPCSAVTGDGLDEGLDWL 155

ADP-ribosylation factor-1 (Arf1) and ADP-ribosylation factor-5 (Arf5); The Arf1-Arf5-like subfamily contains Arf1, Arf2, Arf3, Arf4, Arf5, and related proteins. Arfs1-5 are soluble proteins that are crucial for assembling coat proteins during vesicle formation. Each contains an N-terminal myristoylated amphipathic helix that is folded into the protein in the GDP-bound state. GDP/GTP exchange exposes the helix, which anchors to the membrane. Following GTP hydrolysis, the helix dissociates from the membrane and folds back into the protein. A general feature of Arf1-5 signaling may be the cooperation of two Arfs at the same site. Arfs1-5 are generally considered to be interchangeable in function and location, but some specific functions have been assigned. Arf1 localizes to the early/cis-Golgi, where it is activated by GBF1 and recruits the coat protein COPI. It also localizes to the trans-Golgi network (TGN), where it is activated by BIG1/BIG2 and recruits the AP1, AP3, AP4, and GGA proteins. Humans, but not rodents and other lower eukaryotes, lack Arf2. Human Arf3 shares 96% sequence identity with Arf1 and is believed to generally function interchangeably with Arf1. Human Arf4 in the activated (GTP-bound) state has been shown to interact with the cytoplasmic domain of epidermal growth factor receptor (EGFR) and mediate the EGF-dependent activation of phospholipase D2 (PLD2), leading to activation of the activator protein 1 (AP-1) transcription factor. Arf4 has also been shown to recognize the C-terminal sorting signal of rhodopsin and regulate its incorporation into specialized post-Golgi rhodopsin transport carriers (RTCs). There is some evidence that Arf5 functions at the early-Golgi and the trans-Golgi to affect Golgi-associated alpha-adaptin homology Arf-binding proteins (GGAs).

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                  ....*....|....*....|....
gi 2462598888 361 PWHLQPTCAIIGDGLKEGLEKLHD 384
Cdd:cd04150   135 NWYIQATCATSGDGLYEGLDWLSN 158