Proteoform-resolved profiling of plasminogen activation reveals novel abundant phosphorylation site and primary N-terminal cleavage site

Mol Cell Proteomics. 2023 Dec 13:100696. doi: 10.1016/j.mcpro.2023.100696. Online ahead of print.ABSTRACTPlasminogen, the zymogen of plasmin, is a glycoprotein involved in fibrinolysis and a wide variety of other physiological processes. Plasminogen dysregulation has been implicated in a range of diseases. Classically, human plasminogen is categorized into two types, supposedly having different functional features, based on the presence (type I) or absence (type II) of a single N-linked glycan. Using high-resolution native mass spectrometry (native MS), we uncover that the proteoform profiles of human plasminogen (and plasmin) are substantially more extensive than this simple binary classification. In samples derived from human plasma, we identified up to 14 distinct proteoforms of plasminogen, including a novel, highly stoichiometric phosphorylation site at Ser339. To elucidate the potential functional effects of these post-translational modifications, we performed proteoform-resolved kinetic analyses of the plasminogen-to-plasmin conversion using several canonical activators. This conversion is thought to involve at least two independent cleavage events: one to remove the N-terminal peptide, and another to release the active catalytic site. Our analyses reveal that these processes are not independent but are instead tightly regulated and occur in a step-wise manner. Notably, N-terminal cleavage at the canonical site (Lys77) does not occur directly from intact plasminogen. I...
Source: Molecular and Cellular Proteomics : MCP - Category: Molecular Biology Authors: Source Type: research