Complement C1r subcomponent-like protein (C1RL)

The **complement C1r subcomponent-like protein** (C1RL) is a serine protease homolog structurally similar to the complement C1r subcomponent, which is a component of the classical pathway of the complement system[3][4]. However, C1RL is distinct from the canonical Complement C1r subcomponent. The canonical C1r protein is a Ca2+-dependent serine protease that forms part of the C1 complex in the classical complement pathway, responsible for activating C1s and initiating the cascade leading to pathogen lysis and immune response[3][2][4]. C1RL, despite extensive sequence similarity, is not clearly established as an active protease or as a therapeutic target and does not have a direct function ascribed in complement activation unlike its canonical counterpart. No drugs, disease roles, or biomarker applications are currently attributed to C1RL, and it does not appear in major target databases as a therapeutic target. **Note:** There is **potential confusion between "C1RL" (Complement C1r subcomponent-like protein)** and **"C1R" (Complement C1r subcomponent)**. The latter is a well-established serine protease and part of the C1 complex of the classical complement pathway, whereas C1RL is a "like" or homologous protein with uncertain or undefined biological and clinical roles. Most literature and target databases focus on C1R as the functional protease in the complement system, not C1RL[3][4][1][2]. If the intent was to reference the well-characterized C1R, please specify, as current evidence suggests C1RL is not a validated target and has limited data regarding its biological or pharmacological relevance.

Other names

Complement C1r subcomponent-like proteinC1RLC1RL1C1RLPCLSPAC1r-LPC1r-like proteinCLSPaC1r-like serine protease analog proteincomplement C1r-like proteinasecomplement component 1, r subcomponent-like