Arhgap36 was identified in a genome-scale cDNA overexpression screen as a positive regulator of the Hedgehog pathway that acts independently of Smoothened, inhibiting Gli repressor formation and promoting activation of full-length Gli proteins.

The paper that discovered this gene's Hedgehog function names the residue that replaced the arginine finger and concludes that catalytic GAP function may not be required for its Gli-activating activity.

Two further residues structurally equivalent to those required for Rho GAP function in Graf were mutated without loss of Gli activation.

ARHGAP36 binds the PKA catalytic subunit directly through an N-terminal pseudosubstrate motif, mapped to a 25-residue sequence requiring R153 and R154, which docks into the acidic active-site cleft of PKAC.

Inhibition of PKAC catalysis was measured on purified components, with a PKI peptide as the positive control in the same assay.

The authors' own summary of the inhibition experiments, stated in terms of the PKI comparison.

ARHGAP36 expressed alone concentrates at the plasma membrane, while PKAC is otherwise largely cytosolic and is recruited onto vesicles on coexpression.

The constructs are explicitly the human protein, isoform 2, which is what makes the localisation and inhibition results assignable to Q6ZRI8-2 rather than to an ortholog.

ARHGAP36 lacks the arginine finger conserved in catalytically active RhoGAP homologs and has no effect on the activities of Rac1, Cdc42 or RhoA; residues structurally equivalent to those associated with GTP hydrolysis are not required for its Gli-activating function.

The residue occupying the arginine-finger position is named explicitly, in the numbering of human isoform 2.

The GAP-like domain is retained as a protein interaction module rather than a catalytic one, which is the resolution reached for other non-catalytic RhoGAP-domain proteins.

Isoform 1, the UniProt canonical sequence, behaves differently from the other four: it is perinuclear and does not activate Gli, whereas the others reach the plasma membrane and do.

Patched1 interacts with and stabilises ArhGAP36 at the centrosome, and activating the Shh pathway removes ArhGAP36 from the mother centriole, allowing centrosomal PKA to accumulate.

Knockdown of ArhGAP36 raises PKAc and phosphorylated Inversin, establishing the sign of the endogenous relationship by loss of function rather than by overexpression.

ARHGAP36 is a direct target of the motor-neuron Isl1-Lhx3 complex, and it promotes Gli-dependent transactivation partly by inhibiting PKA activity.

In this paper's own Supplementary Table 2, under the RhoGEF/RhoGAP activity screen columns, ARHGAP36 scores negative for RhoA, negative for Rac1 and negative for Cdc42, while ARHGAP35 (RhoA+, Rac1+) and ARHGAP1 (RhoA+, Cdc42+) score positive in the same run.

Supplementary Table 1 records the screened construct as human isoform 2, 517 aa, and gives the authors' own domain classification for ARHGAP36 verbatim as "GAP-like (arginine finger missing)".

The screen contains known false-negative examples, but the all-negative fraction is not itself a false-negative rate: 15 of its 65 scorable GAP rows are negative for all three GTPases, and ARHGAP17/RICH1, a characterised Cdc42 GAP, is among them. Four of the six arginine-finger-less PROSITE-RhoGAP proteins present in the screen are all-negative, ARHGAP36 included, against that 23 percent base rate.

A systematic survey of the human RHOGAP family found that 9 of the 66 RHOGAP-domain proteins do not have a catalytic domain capable of terminating RHO protein signalling.

Noncoding intergenic duplications at Xq26.1 dysregulate ARHGAP36, and ARHGAP36 protein is elevated in telogen hair follicles, basal cell carcinomas and trichoepitheliomas from affected individuals.

An independent group restates the resolution of the GAP question, that ARHGAP36 acts as a PKA inhibitor rather than on Rho GTPases, and supplies an in vivo readout of PKAC depletion in melanocytes.

FOXC1 directly induces ARHGAP36, and ARHGAP36 in turn depletes PKA and its catalytic subunit, activating Hedgehog signalling and making it less dependent on Smoothened.

ARHGAP36 promotes entotic cell-in-cell formation by binding beta-catenin through its N-terminal arginine-rich domain and, mutually exclusively, interacting with PKAc to activate RhoA signalling and actomyosin contraction.

Accessible primary Fig.8A and supplementary S6-S8 show an actin-associated ARHGAP36 pool and altered polarized F-actin/pMLC2 distribution after target knockdown in MDA-MB-436-10 cells. These contextual data support the inherited actin process and location independently of GAP catalysis.

The authors summarise ARHGAP36 as a RhoGAP signal transduction protein that activates the non-canonical Hedgehog pathway and antagonises PKA signalling, and report that its overexpression drives osteoblast differentiation through that pathway.

UniProt annotates an arginine-finger Site at position 258 of ARHGAP36 by PROSITE ProRule (ECO:0000255) and asserts GTPase activator activity by similarity (ECO:0000250); the residue at 258 is a threonine.

Three controls carrying their own annotated arginine finger all project onto position 258 and each recovers every other control's finger, so the Site is in register; the nearest arginine is 7 residues away.

Mouse Arhgap36 carries the same substitution at its own annotated Site 246, and the human and mouse sites project onto each other reciprocally, so the loss predates the rodent-primate split and lies well below the Eumetazoan node the IBD is placed at.

The GTPase-contacting surface from PDB 1TX4 projects onto ARHGAP36 at 8 of 25 identical positions against 9 of 25 for mouse Arhgap6, so the binding surface is about as conserved as the catalysing family member's while the catalytic residue is not.

Primary images and supplementary legends support contextual actin association and spatial organization; source-level provenance and catalytic-screen limitations are recorded.