# Ras Isoforms from Lab Benches to Lives--What Are We Missing and How Far Are We?
## 5 Missing Pieces in the Ras Puzzle
### Ras and Infection  
The research on the involvement of Ras isoforms in diseases other than cancers is still in its initial stages. [PERSON] et al. showed that H-/K- and N-Ras are differentially involved in _Leishman major_ infection. On infection, the expression of H- and N-Ras increases, whereas that of K-Ras decreases. Upon infection, the activation of N-Ras increased but that of both H- and K-Ras decreased. Higher expression but lower activation of H-Ras were correlated to its retainment in the Golgi possibly due to _Leishman_-induced alteration of palmitoylation. N-Ras silencing using lentivirusally expressed short hairpin RNA or a peptide (designed from the interface of SOS-N-Ras interaction) reduced _Leishman_ infection [113]. The role of Ras isoforms in antigen-specific immune response was also investigated. Using T-dependent and T-independent hapten-carrier conjugates, it was shown that silencing of N-Ras resulted in reduced carrier-specific T cells, reduced IL-4, and increased IFN\(\gamma\) production, whereas reciprocal effects were obtaining on H-/K-Ras silencing. Corroborating with this, N-Ras elicited a TH1 response, whereas H-/K-Ras gave a TH2 response. H-/K-Ras overexpression induced fewer Treg cells in Ovalbumin primed BALB/c mice when compared to N-Ras overexpression. These findings suggest that Ras isoforms can regulate antigen-specific immune responses in T cells [118]. Isoforms Yet Non-Identical-Subtle Structural Difference in-Ras Isoforms--The G-Domain Isn't Identical  
Except for the first 85 amino acids, the rest of the residues in Ras isoforms show only 80% similarity. Owing to these differences, only K-Ras undergo PKC mediated phosphorylation [119]. In addition to the sequence dissimilarities in the HVR region and differential post-translational modification in Ras isoforms, there exists a difference in the G-domain and allosteric lobe too. Emerging studies conducted using wild-type and Ras isoforms bound to GTP analogs have shown that even the G-domain in Ras isoforms are different [120]. There are 17 residues in the G-domain that is different for the isoforms. These differences lie in helix3/loop8 and helix4, between conserved \({}^{116}\)NKCD\({}^{119}\) and \({}^{143}\)ETSAK\({}^{147}\) motifs. Helix 3/loop 7 motif is crucial for connecting the active site of Ras to membrane-interacting residues. Additionally, residue 94 and 95 are different for all three isoforms. Position 95 is occupied by glutamine in H-Ras, histidine in K-Ras, and leucine in N-Ras. All these differences may lead to significant differences in the biochemical properties of Ras isoforms as well as in their signaling output. The allosteric lobe interacts with the effector lobe and there lie isoform-specific differences in the _N_-terminal end of helix3/loop7, loop 8 preceding helix4, and C-terminus of helix 5 [121]. These isoform-specific differences can alter the interaction of the allosteric lobe with the active site of Ras isoforms. Sequence changes in Helix3/loop7 that link the active site to the allosteric site can affect the conformation [122], whereas sequence changes in Helix5 that contain nucleotide-sensor residues R161 and R164 linked to the active site can affect water-mediated hydrogen bonds [123]. Also, the residues near the nucleotide-binding pocket that may dictate the conformational transition of the active site are different in the isoforms. H-Ras has Tyr-141 whereas K and N-Ras have Phe-141. Such differences in residues can impact the configuration of the salt bridge that links the active-site motifs [124]. Isoform-specific residues A/P121, S/T127 for H-Ras, and Y/F141 lie around the salt bridge and may alter the way each isoform interacts in its GTP form. The proximity of these motifs to the residue pocket of Ras may also affect its interaction with the membrane [121]. One study has pointed out that the global conformational exchange of K-Ras-GppNHp is very similar to that of H-Ras [125]. [PERSON] et al.