LRE1 Antibody

What is LRE1 and what is its primary biological function?

LRE1 is a novel sAC-specific inhibitor identified through mass spectrometry-based adenylyl cyclase assays. It functions by binding to the bicarbonate activator binding site and inhibits sAC through a unique allosteric mechanism. LRE1 effectively inhibits sAC-mediated functions in various physiological systems including sperm and mitochondria, making it a valuable tool for exploring intracellular and intraorganellar cAMP microdomains .

How does LRE1 differ from other adenylyl cyclase inhibitors?

Unlike many adenylyl cyclase inhibitors, LRE1 demonstrates exceptional specificity for sAC. Testing confirms it does not inhibit G protein-regulated transmembrane adenylyl cyclases (tmACs) even at concentrations that completely inhibit sAC. This specificity was validated across multiple tmAC isoforms (types I, II, V, VIII, and IX). Additionally, LRE1 tested negative in 17 other in vitro and cell-based screens against various targets including other nucleotidyl cyclases, proteases, ion channels, and receptors . This high specificity makes LRE1 particularly valuable for distinguishing between different adenylyl cyclase contributions in biological processes.

What is the molecular mechanism by which LRE1 inhibits sAC?

LRE1 occupies the HCO₃⁻ binding site (BBS) located between Lys95 and Arg176, both essential for bicarbonate regulation of sAC. Structural analysis at 1.7 Å resolution reveals that LRE1 extends into a channel connecting the BBS to the active site. Kinetic experiments demonstrate that LRE1 inhibition is competitive with HCO₃⁻ but non-competitive with ATP. Though LRE1 does not directly overlap with the substrate binding site, its presence causes significant conformational changes that affect ATP positioning within the active site, forcing it into an orientation incompatible with catalysis .

What specific structural interactions contribute to LRE1's inhibitory effect?

Crystallographic analysis reveals several key interactions:

• The substituted pyrimidine ring of LRE1 occupies a hydrophobic pocket formed by Phe165, Leu166, Leu102, Val167, Met337, and Lys95

• Hydrogen bonds form between the backbone oxygens of Val167 (2.7 Å) and Met337 (2.9 Å) to the amino group of the LRE1 pyrimidine

• The chlorine substituent points into a highly hydrophobic pocket formed by Leu102, Val167, Phe165, Leu166, and side chain carbons of Lys95

• The cyclopropene ring is accommodated in a hydrophobic pocket lined by Phe336 and Phe45/Ala97

• The thiophene ring interacts with Phe45 through a T-shaped π-stacking interaction

These interactions result in unique conformational changes, particularly affecting Arg176, which is reoriented away from the active site, preventing the normal activation mechanism.

How does LRE1 affect mitochondrial function during hepatic ischemia/reperfusion injury?

LRE1 demonstrates significant protective effects against mitochondrial damage during hepatic ischemia/reperfusion (I/R) injury. Pretreatment with LRE1:

• Prevents mitochondrial membrane potential loss caused by I/R

• Increases mitochondrial resilience to membrane permeability transition (mPT) induction by calcium challenge

• Significantly reduces reactive oxygen species (ROS) generation in isolated liver mitochondria

• Induces a mitohormetic response that protects mitochondria from I/R-related insults

These protective effects position LRE1 as a potential therapeutic tool for conditions involving mitochondrial dysfunction during ischemic events.

What molecular changes does LRE1 induce in mitochondrial gene expression?

LRE1 pretreatment triggers significant changes in mitochondrial-associated gene expression following I/R injury:

• Increases expression of genes encoding cytochrome c oxidase (COX) subunits I and IV

• Elevates mitochondrial transcription factor A (TFAM) expression, indicating initiation of mitochondrial biogenesis

• Increases microtubule-associated proteins 1A/1B light chain 3B (LC3b) expression, a regulator of mitophagy

• Shows a trend toward recovery of superoxide dismutase 2 (SOD2) levels, though not reaching statistical significance

• Does not affect peroxisome proliferator-associated receptor gamma coactivator 1α (PGC-1α) expression, possibly due to timing effects as PGC-1α is involved in early phases of mitochondrial biogenesis

These gene expression changes suggest LRE1 may protect against I/R injury by promoting mitochondrial biogenesis and enhancing mitochondrial function.

How can LRE1 be utilized to study sAC-dependent processes in cellular systems?

LRE1 serves as an effective tool for investigating sAC-specific functions in various experimental systems:

• In 4-4 cells (HEK293 cells stably overexpressing sAC), LRE1 inhibits cAMP accumulation with an IC₅₀ of 11 μM

• In pancreatic β cell models (INS-1E cells), LRE1 blocks glucose-induced cAMP response while having minimal effect on basal, tmAC-dependent cAMP synthesis in low glucose conditions

• In sperm, LRE1 concentration-dependently blocks PKA-dependent phosphorylation, tyrosine phosphorylation, hyperactivation, and fertilization capacity

These applications demonstrate LRE1's utility in dissecting sAC-dependent from tmAC-dependent cAMP signaling in complex biological systems.

What considerations should be taken when designing LRE1-based experiments?

When designing experiments with LRE1, researchers should consider:

• Effective concentration range: LRE1 typically shows optimal sAC inhibition at 10-50 μM in cellular systems

• Specificity controls: Include experiments in sAC knockout models or with other adenylyl cyclase activators to confirm specificity

• Temporal factors: Some gene expression changes may occur at different time points following LRE1 treatment

• Cellular context: The relative contributions of sAC versus tmACs to cAMP production varies by cell type

• Downstream readouts: Monitor specific sAC-dependent processes (PKA activation, mitochondrial function) to confirm LRE1 effects

How does LRE1 compare with KH7, another sAC-specific inhibitor?

Both LRE1 and KH7 are sAC-specific inhibitors, but they differ in several important aspects:

• Specificity: Both compounds show specificity for sAC over tmACs

• Potency: They exhibit comparable IC₅₀ values for inhibiting sAC activity

• Toxicity: LRE1 demonstrates significantly lower toxicity compared to KH7, which exhibits cellular toxicity at low μM concentrations after 2 days in culture

• Mechanistic differences: While both target sAC specifically, they may have different binding modes and conformational effects

The improved toxicity profile of LRE1 makes it particularly valuable for long-term studies and potential therapeutic applications.

What advantages does LRE1 offer for studying mitochondrial function?

LRE1 provides several advantages for studying mitochondrial sAC functions:

• Unlike some compounds that can uncouple mitochondria or cause non-specific toxicity, LRE1 appears to specifically inhibit mitochondrial sAC without these side effects

• It effectively prevents mitochondrial swelling and ROS generation during stress conditions

• LRE1 pretreatment preserves SirT3 levels and reduces acetylated lysine residues in mitochondrial preparations, suggesting maintenance of mitochondrial OXPHOS capacity

• These properties allow researchers to specifically study the role of sAC in mitochondrial function without confounding effects from mitochondrial toxicity

How might LRE1 be applied in translational research models?

Based on its protective effects in hepatic I/R models and specificity for sAC, LRE1 shows promise for several translational applications:

• Organ preservation during transplantation procedures

• Protective strategies for ischemic events including stroke and myocardial infarction

• Management of acute kidney injury and other ischemia-related pathologies

• Exploration of sAC inhibition as a novel therapeutic strategy for conditions involving mitochondrial dysfunction

Further research is needed to fully characterize LRE1's efficacy and safety profile in various disease models before clinical translation.

What methodological approaches can validate LRE1-specific effects in experimental systems?

To ensure observed effects are specifically due to sAC inhibition by LRE1, researchers should employ multiple validation approaches:

• Genetic controls: Compare LRE1 effects in wild-type versus sAC knockout systems

• Rescue experiments: Attempt to rescue LRE1 effects with membrane-permeable cAMP analogs

• Dose-response characterization: Establish clear concentration-dependent effects correlating with sAC inhibition

• Alternative inhibitors: Compare effects with other sAC inhibitors like KH7 to confirm mechanism-specific rather than compound-specific effects

• Specific biochemical readouts: Monitor known sAC-dependent downstream events such as PKA substrate phosphorylation

These methodological considerations help ensure that experimental outcomes can be confidently attributed to LRE1's specific inhibition of sAC rather than off-target effects.