Editing GTPase (section)

=====Small GTPases=====
{{Main|Small GTPase}}
[[Small GTPase]]s function as monomers and have a molecular weight of about 21 kilodaltons that consists primarily of the GTPase domain.<ref name="pmid11152757">{{cite journal |last1=Takai |first1=Y |last2=Sasaki |first2=T |last3=Matozaki |first3=T |date=2001 |title=Small GTP-binding proteins |journal=Physiological Reviews |volume=81 |issue=1 |pages=153–208 |doi=10.1152/physrev.2001.81.1.153 |pmid=11152757 }}</ref> They are also called small or monomeric guanine nucleotide-binding regulatory proteins, small or monomeric GTP-binding proteins, or small or monomeric G-proteins, and because they have significant homology with the first-identified such protein, named [[Ras (protein)|Ras]], they are also referred to as [[Ras superfamily]] GTPases. Small GTPases generally serve as molecular switches and signal transducers for a wide variety of cellular signaling events, often involving membranes, vesicles or cytoskeleton.<ref name="pmid2116664">{{cite journal |last1=Hall |first1=A |date=1990 |title=The cellular functions of small GTP-binding proteins |journal=Science |volume= 249|issue=4969 |pages=635–640 |doi=10.1126/science.2116664 |pmid=2116664 |bibcode=1990Sci...249..635H }}</ref><ref name="pmid11152757"/> According to their primary amino acid sequences and biochemical properties, the many Ras superfamily small GTPases are further divided into five subfamilies with distinct functions: [[Ras (protein)|Ras]], [[Rho family of GTPases|Rho]] ("Ras-homology"), [[Rab (G-protein)|Rab]], [[ADP ribosylation factor|Arf]] and [[Ran protein|Ran]].<ref name="pmid11152757"/> While many small GTPases are activated by their GEFs in response to intracellular signals emanating from cell surface receptors (particularly [[growth factor receptor]]s), regulatory GEFs for many other small GTPases are activated in response to intrinsic cell signals, not cell surface (external) signals.