Recombinant Rat Diacylglycerol O-acyltransferase 2 (Dgat2)

What is the biological role of DGAT2 in lipid metabolism?

DGAT2 catalyzes the final and committed step in triacylglycerol (TAG) synthesis by converting diacylglycerol and acyl-CoA to triacylglycerol. This enzyme plays a critical role in lipid metabolism, particularly in energy storage as fat. Genetic knockdown or pharmacological inhibition of DGAT2 leads to decreased very-low-density lipoprotein TAG secretion and reduced hepatic lipid levels in rodents, indicating its potential as a therapeutic target for hyperlipidemia and hepatic steatosis . DGAT2 is essential for survival in vivo, unlike DGAT1, underscoring its fundamental importance in lipid homeostasis .

How does the structure of DGAT2 relate to its enzymatic activity?

DGAT2 contains highly conserved structural elements across species from yeast to humans. The most critical structural feature is the HPHG sequence (amino acids 161-164 in mouse DGAT2), which is preserved across species . Mutations in this sequence significantly reduce DGAT activity in vitro, suggesting these amino acids form part of the active site . Histidine residues, particularly H161 and H163, are critical for binding certain inhibitors and likely play a role in catalytic activity . When these residues were mutated to alanine (H161A and H163A), binding of imidazopyridine inhibitors dramatically decreased to 11-17% of wild-type enzyme levels, confirming their importance in substrate recognition and catalysis .

What distinguishes DGAT2 from DGAT1 in terms of substrate preference and enzyme kinetics?

Despite catalyzing the same reaction, DGAT1 and DGAT2 exhibit significant differences:

DGAT2 from M. ramanniana exhibits higher activities with diacylglycerols containing short and medium-chain fatty acyl moieties (C6:0, C8:0, and C10:0) compared to longer chains . Available data suggests DGAT2 is a more potent enzyme with higher substrate affinity than DGAT1 .

What are optimal conditions for reconstituting and storing recombinant DGAT2?

For optimal reconstitution of recombinant DGAT2:

• Reconstitute in 10mM PBS (pH 7.4) to a concentration of 0.1-1.0 mg/mL

• Avoid vortexing during reconstitution as this may compromise protein structure and activity

• For short-term storage, keep at 2-8°C for up to one month

• For long-term storage, aliquot the protein and store at -80°C for up to 12 months

• Avoid repeated freeze/thaw cycles to maintain protein stability and activity

The stability of recombinant DGAT2 can be assessed through accelerated thermal degradation tests to determine loss rate over time . Including stabilizers such as trehalose (5%) in buffer formulations can improve protein stability during freeze-drying and storage .

How can researchers design effective knockdown experiments for DGAT2?

For effective DGAT2 knockdown studies:

• Design multiple shRNAs targeting different regions of the DGAT2 CDS sequence

• Verify target specificity using BLAST to prevent off-target effects

• Include appropriate non-targeting controls (shRNA-NC)

• When using adenoviral vectors for shRNA delivery:

  • Ensure approximately 80% cell confluency at time of infection

  • Allow 24 hours post-infection before inducing differentiation

  • Collect samples after sufficient culture time (e.g., 96 hours) for functional assays

Previous studies have successfully designed shRNAs targeting different positions of DGAT2 (e.g., DGAT2-shRNA-108, DGAT2-shRNA-320, and DGAT2-shRNA-687) . Validation of knockdown efficiency through qPCR and Western blot is essential before proceeding with functional assays.

What expression systems are most effective for producing functional recombinant DGAT2?

For recombinant DGAT2 production:

• Prokaryotic systems: E. coli expression systems have been successfully used for producing recombinant human DGAT2 (typically fragments rather than full-length protein) . These systems typically include:

  • N-terminal His-Tag for purification

  • Expression of specific domains (e.g., Arg268-Phe377 of human DGAT2)

  • Buffer formulation containing 0.01% SKL and 5% trehalose for stability

• Eukaryotic systems: For overexpression studies in mammalian cells, adenoviral vectors have proven effective:

  • Construct recombinant shuttle plasmids containing DGAT2 cDNA

  • Use restriction sites (e.g., EcoRI and BamHI) for correct orientation

  • Co-transfect with packaging plasmids in 293A cells

  • Use GFP-expressing adenovirus (Ad-GFP) as control

The choice of expression system depends on the research question, with prokaryotic systems being suitable for structural studies and eukaryotic systems preferable for functional analyses requiring proper folding and post-translational modifications.

How can researchers characterize the enzyme kinetics and inhibition mechanisms of DGAT2?

To characterize DGAT2 enzyme kinetics and inhibition:

• For basic kinetic parameters:

  • Measure initial reaction rates with varying substrate concentrations

  • Determine Km and Vmax values using appropriate plots

  • Compare activity with different acyl-CoA substrates to assess specificity

• For inhibition mechanisms:

  • Pre-incubate enzyme with potential inhibitors before adding substrates

  • For time-dependent inhibitors, vary pre-incubation times

  • Perform detailed kinetic analysis to determine inhibition mode

Studies with imidazopyridine inhibitors like PF-06424439 revealed a two-step binding mechanism with DGAT2:

• Initial enzyme-inhibitor complex (EI) forms

• Complex undergoes isomerization to a higher-affinity state (EI*)

• Resulting complexes have Ki* values of approximately 16-17 nM

• Dissociation half-lives of 1.0-1.2 hours indicate long residence time

These inhibitors demonstrate noncompetitive inhibition with respect to the acyl-CoA substrate, suggesting they bind at a site distinct from the acyl-CoA binding pocket .

What role does DGAT2 play in viral replication, and how can this be experimentally investigated?

Recent research has uncovered an unexpected role for DGAT2 in viral replication, particularly for SARS-CoV-2:

• Mechanism of action:

  • SARS-CoV-2 nucleocapsid protein drives DGAT gene expression

  • This facilitates lipid droplet formation necessary for viral replication

  • Viral nucleocapsid protein associates with adipocyte differentiation-related protein (ADRP) on lipid droplet surfaces

  • DGAT depletion reduces viral protein synthesis without affecting viral genome replication/transcription

• Experimental approaches:

  • siRNA knockdown of DGAT1/DGAT2 in virus-permissive cells (e.g., Caco-2, Calu-3)

  • Pharmacological inhibition using DGAT inhibitors (e.g., xanthohumol)

  • Immunofluorescence visualization of lipid droplet formation and viral protein expression

  • Co-immunoprecipitation to investigate protein-protein interactions

  • Reporter gene assays to detect transcriptional activation of DGAT

Studies have shown that both DGAT1 and DGAT2 are important for SARS-CoV-2 replication, with the virus exhibiting generally higher dependence on DGAT1 than DGAT2 . The DGAT inhibitor xanthohumol demonstrated dose-dependent reduction of virus titers in cell culture and suppressed SARS-CoV-2 replication and associated pulmonary inflammation in a hamster model .

How does DGAT2 overexpression affect gene expression and cellular signaling pathways?

Transcriptome analysis of cells overexpressing DGAT2 reveals complex effects on gene expression and signaling:

• Differential gene expression:

  • DGAT2 overexpression in bovine skeletal muscle satellite cells (BSCs) led to 598 differentially expressed genes (DEGs)

  • These included 292 upregulated and 306 downregulated genes

• Affected pathways: KEGG enrichment analysis showed that DEGs after DGAT2 overexpression were primarily enriched in:

  • PPAR signaling pathway

  • Fat digestion and absorption

  • Glycerophospholipid metabolism

  • Fatty acid biosynthesis

  • AMPK signaling pathway

• Phenotypic effects:

  • Increased cellular triacylglycerol content

  • Upregulation of genes involved in lipid accumulation and adipogenesis

  • Enhanced lipid droplet formation

These findings highlight DGAT2's regulatory role during adipogenic transdifferentiation and the complexity of intramuscular adipogenesis, with implications for applications such as producing high marbling content beef and understanding metabolic disorders .

What controls should be included in DGAT2 functional studies?

Rigorous controls are essential for reliable DGAT2 functional studies:

• For overexpression studies:

  • Empty vector control (Ad-NC)

  • GFP-expressing vector control (Ad-GFP)

  • Verification of expression by qPCR and Western blot

• For knockdown experiments:

  • Non-targeting shRNA control (sh-NC)

  • Multiple shRNAs targeting different regions of DGAT2

  • Verification of knockdown efficiency

• For enzyme activity assays:

  • Substrate blanks (no enzyme)

  • Known DGAT inhibitors as positive controls

  • Wild-type vs. mutant enzyme comparisons (e.g., H161A, H163A mutations)

• For infection/transfection optimization:

  • Cell viability assessments

  • Dose-response curves for viral MOI or plasmid concentration

  • Time-course analyses to determine optimal post-infection/transfection intervals

How can researchers distinguish between the contributions of DGAT1 and DGAT2 in experimental systems?

To distinguish between DGAT1 and DGAT2 functions:

• Selective inhibition:

  • Use isoform-selective inhibitors

  • For imidazopyridines, binding is dramatically reduced in DGAT2 mutants (H161A, H163A)

  • Monitor residual DGAT activity after selective inhibition

• Genetic approaches:

  • Selective knockdown using siRNA/shRNA targeting either DGAT1 or DGAT2

  • Double knockdown to assess additive or synergistic effects

  • Rescue experiments with wild-type or mutant constructs

• Substrate specificity:

  • Utilize the differential substrate preferences (DGAT1 prefers monounsaturated substrates)

  • Compare enzyme activity with different acyl-CoA chain lengths

• Expression pattern analysis:

  • Analyze tissue-specific expression patterns

  • Evaluate differential responses to stimuli

What are common technical challenges when working with recombinant DGAT2 and how can they be addressed?

Common technical challenges and solutions include:

• Protein instability:

  • Store at 2-8°C for short-term (up to one month)

  • For long-term storage, prepare aliquots and store at -80°C

  • Avoid repeated freeze/thaw cycles

  • Include stabilizers such as trehalose (5%) in formulations

• Expression difficulties:

  • For E. coli expression, consider expressing specific domains (e.g., Arg268-Phe377) rather than full-length protein

  • Use appropriate tags (e.g., N-terminal His-Tag) to facilitate purification

  • Optimize buffer conditions (e.g., PBS pH 7.4)

• Activity measurement challenges:

  • Ensure complete reconstitution without vortexing

  • Use fresh preparations when possible

  • Include appropriate controls in enzyme assays

  • Consider enzyme concentration effects on activity

• Experimental variability:

  • Standardize cell culture conditions

  • Control cell confluence (approximately 80%) for infection/transfection

  • Allow sufficient time post-infection before functional assays (e.g., 96 hours)

  • Verify protein expression/knockdown before functional studies

What emerging therapeutic applications exist for DGAT2 inhibitors?

DGAT2 inhibitors show promise for multiple therapeutic applications:

• Metabolic disorders:

  • Treatment of hyperlipidemia and hepatic steatosis

  • Genetic knockdown or pharmacological inhibition reduces very-low-density lipoprotein TAG secretion and hepatic lipid levels in rodents

• Antiviral applications:

  • DGAT inhibitors like xanthohumol suppress SARS-CoV-2 replication

  • Reduce associated pulmonary inflammation in animal models

  • May offer a novel host-directed antiviral strategy

• Mechanism-based advantages:

  • Long residence time inhibitors (e.g., imidazopyridines PF-06424439)

  • Two-step binding mechanism with slow dissociation (half-lives of 1.0-1.2 hours)

  • Noncompetitive inhibition with respect to acyl-CoA substrate

The development of selective DGAT2 inhibitors with high oral bioavailability represents a promising approach for these therapeutic applications, particularly given DGAT2's potency and substrate affinity .

How does mutation of the conserved HPHG motif affect DGAT2 function, and what are the implications for structure-based drug design?

The HPHG motif (amino acids 161-164 in mouse DGAT2) is highly conserved across species from yeast to humans and critical for enzyme function:

• Functional significance:

  • Mutations in this sequence significantly reduce DGAT activity in vitro

  • Suggests these amino acids may form part of the active site

  • Histidine residues may play a catalytic role, similar to acyltransferase enzymes of the MBOAT family

• Inhibitor binding:

  • Binding of imidazopyridine inhibitors is dramatically reduced in DGAT2 mutants (H161A, H163A)

  • Only 11-17% of wild-type binding remains in these mutants

  • Indicates these residues are critical for inhibitor recognition

• Implications for drug design:

  • Structure-based design should focus on interactions with the HPHG motif

  • Potential for development of more selective inhibitors targeting this region

  • May allow rational design of inhibitors with enhanced potency or modified pharmacokinetic properties

Understanding the structural basis of the HPHG motif's role in catalysis and inhibitor binding could facilitate the development of next-generation DGAT2 inhibitors with improved properties.

What advanced methodologies are enhancing our understanding of DGAT2's role in lipid metabolism and disease states?

Cutting-edge approaches advancing DGAT2 research include:

• Transcriptomic analysis:

  • Identification of differentially expressed genes after DGAT2 modulation

  • Pathway enrichment analysis revealing complex metabolic networks

  • Elucidation of DGAT2's role in PPAR signaling, glycerolipid metabolism, and fatty acid biosynthesis

• Advanced imaging techniques:

  • Visualization of lipid droplet formation and DGAT2 localization

  • Quantification of changes in lipid droplet size, number, and distribution

  • Co-localization studies with other proteins involved in lipid metabolism

• Protein-protein interaction studies:

  • Co-immunoprecipitation to identify interaction partners

  • Investigation of DGAT2's role in multiprotein complexes

  • Understanding of interactions with viral proteins (e.g., SARS-CoV-2 nucleocapsid protein)

• In vivo models:

  • Evaluation of DGAT inhibitors in animal models

  • Assessment of effects on lipid metabolism and disease progression

  • Testing of anti-viral efficacy in infection models

These methodologies continue to reveal DGAT2's complex roles beyond its canonical function in triglyceride synthesis, including unexpected roles in viral replication and inflammation.