Comparative Nucleotide-Dependent Interactome Analysis Reveals Shared and Differential Properties of KRas4a and KRas4b

The KRAS gene encodes two isoforms, KRas4a and KRas4b. Differences in the signaling functions of the two KRas proteins are poorly understood. Here we report the comparative and nucleotide-dependent interactomes of KRas4a and KRas4b. Many previously unknown interacting proteins were identified, with some interacting with both isoforms while others prefer only one. For example, v-ATPase a2 and eIF2Bδ interact with only KRas4b. Consistent with the v-ATPase interaction, KRas4b has a significant lysosomal localization. Comparing WT and constitutively active G12D mutant KRas, we examined differences in the effector proteins of the KRas4a and KRas4b. Interestingly, KRas4a binds RAF1 stronger than KRas4b. Correspondingly, KRas4a can better promote ERK phosphorylation and anchorage-independent growth than KRas4b. The interactome data represent a useful resource to understand the differences between KRas4a and KRas4b and to discover new function or regulation for them. A similar proteomic approach would be useful for studying numerous other small GTPases

Comparative Nucleotide-Dependent Interactome Analysis Reveals Shared and Differential Properties of KRas4a and KRas4b

The KRAS gene encodes two isoforms, KRas4a and KRas4b. Differences in the signaling functions of the two KRas proteins are poorly understood. Here we report the comparative and nucleotide-dependent interactomes of KRas4a and KRas4b. Many previously unknown interacting proteins were identified, with some interacting with both isoforms while others prefer only one. For example, v-ATPase a2 and eIF2Bδ interact with only KRas4b. Consistent with the v-ATPase interaction, KRas4b has a significant lysosomal localization. Comparing WT and constitutively active G12D mutant KRas, we examined differences in the effector proteins of the KRas4a and KRas4b. Interestingly, KRas4a binds RAF1 stronger than KRas4b. Correspondingly, KRas4a can better promote ERK phosphorylation and anchorage-independent growth than KRas4b. The interactome data represent a useful resource to understand the differences between KRas4a and KRas4b and to discover new function or regulation for them. A similar proteomic approach would be useful for studying numerous other small GTPases

HDAC8 Catalyzes the Hydrolysis of Long Chain Fatty Acyl Lysine

The histone deacetylase (HDAC) family regulates many biological pathways through the deacetylation of lysine residues on histone and nonhistone proteins. Mammals have 18 HDACs that are classified into four classes. Class I, II, and IV are zinc-dependent, while class III is nicotinamide adenine dinucleotide (NAD⁺)-dependent lysine deacetylase or sirtuins. HDAC8, a class I HDAC family member, has been shown to have low deacetylation activity compared to other HDACs <i>in vitro.</i> Recent studies showed that several sirtuins, with low deacetylase activities, can actually hydrolyze other acyl lysine modifications more efficiently. Inspired by this, we tested the activity of HDAC8 using a variety of different acyl lysine peptides. Screening a panel of peptides with different acyl lysine modifications, we found that HDAC8 can catalyze the removal of acyl groups with 2–16 carbons from lysine 9 of the histone H3 peptide (H3K9). Interestingly, the catalytic efficiencies (<i>k</i>_cat/<i>K</i>_m) of HDAC8 on octanoyl, dodecanoyl, and myristoyl lysine are several-fold better than that on acetyl lysine. The increased catalytic efficiencies of HDAC8 on larger fatty acyl groups are due to the much lower <i>K</i>_m values. T-cell leukemia Jurkat cells treated with a HDAC8 specific inhibitor, PCI-34051, exhibited an increase in global fatty acylation compared to control treatment. Thus, the de-fatty-acylation activity of HDAC8 is likely physiologically relevant. This is the first report of a zinc-dependent HDAC with de-fatty-acylation activity, and identification of HDAC8 de-fatty-acylation targets will help to further understand the function of HDAC8 and protein lysine fatty acylation