Extracellular and plasma protein substrates

Extracellular and plasma protein substrates represent a broad, heterogeneous category of proteins located outside of cells, primarily within the blood plasma or the interstitial extracellular matrix (ECM) (StatPearls, https://www.ncbi.nlm.nih.gov/books/NBK541071/). This group includes essential physiological components such as coagulation factors (e.g., fibrinogen, prothrombin), transport proteins (e.g., albumin), and structural proteins (e.g., collagen, laminin) that serve as the primary targets for various enzymes like proteases and kinases (Nature Reviews Molecular Cell Biology, https://www.nature.com/articles/s41580-018-0023-y). In pharmacology, this classification is often used to group drugs that do not target a specific cellular receptor or enzyme but instead interact with circulating or structural proteins to modulate processes like blood clotting, inflammation, and tissue architecture (IUPHAR/BPS Guide to Pharmacology, https://www.guidetopharmacology.org/). For example, thrombolytic agents like alteplase act by activating the substrate plasminogen, while heparin exerts its anticoagulant effect by binding to the plasma protein antithrombin III. Because this term encompasses a vast array of distinct molecular entities rather than a single receptor or enzyme, it is considered a functional or localization-based category rather than a specific therapeutic target (ChEMBL, https://www.ebi.ac.uk/chembl/).

Other names

Plasma proteinsExtracellular matrix proteinsCirculating protein substratesNon-cellular protein targets

Drugs targeting these substrates typically function by binding to the protein to prevent its activation, acting as a replacement for a deficient protein, or enzymatically modifying the substrate to alter its physiological activity, such as promoting the degradation of fibrin in thrombolysis.