Cryptosporidiosis accounts for a surge in infant (<5 years) mortality and morbidity. To date, several drug discovery efforts have been put in place to develop effective therapeutic options against the causative parasite. Based on a recent report, P131 spares inosine monophosphate dehydrogenase (IMPDH) in a eukaryotic model (mouse IMPDH (mIMPDH)) while binding selectively to the NAD⁺ site in Cryptosporidium parvum (CpIMPDH). However, no structural detail exists on the underlining mechanisms of P131-CpIMPDH selective targeting till date. To this effect, we investigate the selective inhibitory dynamics of P131 in CpIMPDH relative to mIMPDH via molecular biocomputation methods. Pairwise sequence alignment revealed prominent variations at the NAD⁺ binding regions of both proteins that accounted for disparate P131 binding activities. The influence of these variations was further revealed by the MM/PBSA energy estimations coupled with per-residue energy decomposition which monitored the systematic binding of the compound. Furthermore, relative high-affinity interactions occurred at the CpIMPDH NAD⁺ site which were majorly mediated by SER22, VAL24, PRO26, SER354, GLY357, and TYR358 located on chain D. These residues are unique to the parasite IMPDH form and not in the eukaryotic protein, highlighting variations that account for preferential P131 binding. Molecular insights provided herein corroborate previous experimental reports and further underpin the basis of CpIMPDH inhibitor selectivity. Findings from this study could present attractive prospects toward the design of novel anticryptosporidials with improved selectivity and binding affinity against parasitic targets.

隐孢子虫病导致婴儿（<5岁）死亡率和发病率激增。迄今为止，已经进行了数种药物发现工作来开发针对病原性寄生虫的有效治疗选择。根据最近的报道，P131在真核模型（小鼠IMPDH（m IMPDH））中保留了肌苷单磷酸脱氢酶（IMPDH），同时选择性地结合了小隐孢子虫（Cp IMPDH）的NAD ⁺位点。然而，到目前为止，关于P131- Cp IMPDH选择性靶向作用的机制尚无结构细节。为此，我们研究了Cp IMPDH中P131相对于m的选择性抑制动力学IMPDH通过分子生物计算方法。成对序列比对揭示了两种蛋白质的NAD ⁺结合区的显着差异，这说明了不同的P131结合活性。MM / PBSA能量估算与每个残基能量分解（结合监测化合物的系统结合）一起进一步揭示了这些变化的影响。此外，在Cp IMPDH NAD ⁺处发生了相对高亲和力的相互作用该位点主要由位于链D上的SER22，VAL24，PRO26，SER354，GLY357和TYR358介导。这些残基是寄生虫IMPDH形式所特有的，而不是在真核蛋白中，突出显示了优先P131结合的变异。本文提供的分子见解证实了先前的实验报告，并进一步巩固了Cp IMPDH抑制剂选择性的基础。这项研究的结果可能会为新型抗隐孢子虫的设计提供有吸引力的前景，该抗隐孢子虫具有提高的选择性和对寄生虫靶标的结合亲和力。