Department of Chemistry, Durham University, Lower Mountjoy, Durham, County Durham, United Kingdom.
Bio-Prodict, Nijmegen, The Netherlands.
J Biol Chem. 2022 May;298(5):101919. doi: 10.1016/j.jbc.2022.101919. Epub 2022 Apr 8.
The Candidate Phyla Radiation is a recently uncovered and vast expansion of the bacterial domain of life, made up of largely uncharacterized phyla that lack isolated representatives. This unexplored territory of genetic diversity presents an abundance of novel proteins with potential applications in the life-science sectors. Here, we present the structural and functional elucidation of CPR-C4, a hypothetical protein from the genome of a thermophilic Candidate Phyla Radiation organism, identified through metagenomic sequencing. Our analyses revealed that CPR-C4 is a member of a family of highly conserved proteins within the Candidate Phyla Radiation. The function of CPR-C4 as a cysteine protease was predicted through remote structural similarity to the Homo sapiens vasohibins and subsequently confirmed experimentally with fluorescence-based activity assays. Furthermore, detailed structural and sequence alignment analysis enabled identification of a noncanonical cysteine-histidine-leucine(carbonyl) catalytic triad. The unexpected structural and functional similarities between CPR-C4 and the human vasohibins suggest an evolutionary relationship undetectable at the sequence level alone.
候选门辐射是细菌生命领域最近发现的一个巨大扩张，由大量未被表征的门组成，这些门缺乏孤立的代表。这个未经探索的遗传多样性领域提供了丰富的新型蛋白质，具有在生命科学领域应用的潜力。在这里，我们通过宏基因组测序，从一个嗜热候选门辐射生物的基因组中鉴定出一个假定蛋白 CPR-C4，对其进行了结构和功能的阐明。我们的分析表明，CPR-C4 是候选门辐射中高度保守蛋白家族的一员。通过与人类血管抑肽的远程结构相似性预测了 CPR-C4 作为半胱氨酸蛋白酶的功能，随后通过基于荧光的活性测定实验得到了证实。此外，详细的结构和序列比对分析确定了一个非典型的半胱氨酸-组氨酸-亮氨酸（羰基）催化三联体。CPR-C4 与人类血管抑肽之间出人意料的结构和功能相似性表明，仅通过序列水平无法检测到进化关系。
