A lysyl oxidase (LOX)/bone morphogenetic protein-1 (BMP1) complex to facilitate collagen remodeling

Collagen biosynthesis within the extracellular matrix (ECM) relies on finely regulated enzymatic steps to ensure proper collagen maturation and fibrillar assembly. Among these, bone morphogenetic protein-1 (BMP1) and the canonical lysyl oxidase (LOX) act on the collagen telopeptide to promote procollagen processing and oxidative cross-linking, respectively. However, the mechanisms that ensure precise coordination of their activities remain poorly understood. Using NanoBiT assays, we identified and characterized a stable LOX/BMP1 protein complex that assembles intracellularly during trafficking through the ER/Golgi pathway and persists after secretion. Analysis of BMP1 and LOX domains involved in the interaction showed that BMP1 binding requires its CUB2/3 domains, while LOX recognition depends on a conserved, positively charged segment of LOX (residues 259-285) located immediately upstream of its catalytic domain. Formation of the LOX/BMP1 complex did not substantially alter LOX enzymatic activity but markedly enhanced LOX association with collagen type I through the carboxy-telopeptide region, facilitating the assembly of a ternary LOX/BMP1/collagen complex. This pre-assembled complex promoted efficient targeting of LOX to nascent collagen fibrils. Our findings reveal a previously unrecognized layer of regulation in collagen biosynthesis, in which LOX and BMP1 act as a functional unit to ensure precise localization and proper processing of collagen. This mechanism offers new insights into ECM assembly and identifies the LOX/BMP1 interface as a potentially druggable node for anti-fibrotic strategies.