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Cover Picture: Protease-Activatable Collagen Targeting Based on Protein Cyclization (ChemBioChem 12/2010)
The cover picture shows a cyclic collagen binding protein, CNA35, that only becomes active after proteolytic cleavage, thereby providing a dual-specific targeting probe for imaging ECM remodeling. CNA35 consists of two domains connected through a flexible linker that bind collagen in a unique way by “wrapping” around a single collagen triple helix. Connecting the N and C termini through an MMP cleavage site yields a cyclic protein that can still form a pseudorotaxane structure that binds to the ends of loose collagen triple helices, but is topologically inhibited from binding to the majority of binding sites present in native collagen. This inhibition can be relieved through cleavage of the cyclic protein by MMP-1; this provides a new targeting strategy that integrates two different markers of ECM remodeling. For more information, see the Communication by M. Merkx et al. on p. 1665 ff. Illustration: ICMS Animation Studio, TU/e.