Synchrotron SAXS data from solutions of the domain-stapled mutant of pro-matrix metalloproteinase-1 (proMMP-1 S243C, S318C) in 50 mM Tris-HCl, 150 mM NaCl, 10 mM CaCl2, pH 7.4 were collected using size-exclusion chromatography SAXS (SEC-SAXS) on the B21 beam line at the Diamond Light Source (Oxfordshire, UK) using a Pilatus 2M detector at a sample-detector distance of 3.9 m and at a wavelength of λ = 0.1 nm (I(s) vs s, where s = 4πsinθ/λ, and 2θ is the scattering angle). SEC-SAXS was performed at 25 °C using the following parameters: Shodex Kw-403 analytical SEC column; Flow rate: 0.2 mL/min; Sample injection concentration: 5.6 mg/mL; Injection volume: 50 μL. The data were collected through the SEC peak of the sample as a series of 28 x 3 second exposures. Each unsubtracted data frame was normalised to the intensity of the transmitted beam and radially averaged and the scattering of an appropriate solvent-blank was subtracted. The resulting subtracted frames were scaled and averaged to generate the final SAXS profile displayed in this entry.