Inosine monophosphate dehydrogenase 1 (IMPDH1) plays a pivotal role in the de novo synthesis of guanine nucleotides by catalyzing the oxidation of inosine monophosphate (IMP) to xanthosine monophosphate (XMP), with concomitant reduction of NAD⁺. Defects in this enzyme are linked to retinitis pigmentosa type 10 (RP10), a hereditary retinal degenerative disorder characterized by progressive vision loss. While IMPDH1 is ubiquitously expressed, mutations in its retinal isoforms selectively impair retinal function, suggesting tissue-specific regulatory mechanisms. The major retinal isoforms of mouse IMPDH1—mH1(514), mH1(546), and mH1(603)—differ from the canonical form by possessing unique N- and C-terminal extensions generated through alternative splicing. This study investigates how these terminal peptide extensions influence the catalytic activity and oligomerization behavior of retinal IMPDH1 isoforms.
Using recombinant expression in *E. coli*, purified mH1 isoforms were subjected to kinetic analysis under varying concentrations of IMP and NAD⁺. The results revealed that the mH1(603) isoform exhibited significantly higher catalytic activity compared to both mH1(514) and mH1(546), as evidenced by increased Vmax values in Hanes-Wolff plots.CD33 Antibody References Notably, no substrate inhibition was observed for any retinal isoform at elevated NAD⁺ levels, contrasting with earlier reports on canonical forms.LMNB2 Antibody web This enhanced activity suggests a functional advantage conferred by the extended termini, possibly related to improved substrate binding or conformational dynamics.
Structural modeling via molecular dynamics simulations indicated that the C-terminal extension of mH1(603) interacts directly with residues near the IMP-binding site and the catalytic flap region—the so-called “finger domain.PMID:34979130 ” These interactions may stabilize the active conformation of the enzyme, thereby increasing catalytic efficiency. Furthermore, gel filtration chromatography demonstrated that mH1(603) formed smaller oligomeric complexes in the presence of ATP, indicating reduced propensity for high-mass aggregation. In contrast, mH1(514) and mH1(546) displayed greater mass accumulation under similar conditions, suggesting that the terminal extensions modulate oligomerization states.
Molecular docking studies revealed that the N-terminal tail of mH1(603) forms a protective layer over the tetramer surface, potentially shielding hydrophobic interfaces involved in octamer formation. This structural feature likely reduces the likelihood of aberrant fibrillation, particularly under stress-inducing conditions such as ATP exposure. Indeed, computational models predict diminished inter-tetramer hydrophobic interactions in mH1(603), consistent with experimental observations of attenuated fibril formation.
Collectively, these findings demonstrate that terminal peptide extensions in retinal IMPDH1 isoforms serve dual roles: enhancing catalytic performance and suppressing pathological aggregation. These adaptations may reflect evolutionary optimization for the retina’s high metabolic demands and susceptibility to oxidative stress. The mH1(603) isoform, being the most abundant in murine retina, appears uniquely equipped to maintain efficient purine biosynthesis while minimizing the risk of protein misfolding—a critical balance for photoreceptor survival. This work provides compelling evidence that structural variations in terminal domains are not merely vestigial but actively contribute to functional specialization within the retinal environment.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com
