A Novel Metalloproteinase,Almelysin, from a Marine Bacterium,Alteromonas sp. No. 3696: Purification and Characterization

We have discovered a novel metalloproteinase, which has high activity at low temperatures, from the culture supernatant of a marine bacterium. The strain was identified as Alteromonas sp. No. 3696. The metalloproteinase, named almelysin, was purified to homogeneity from the cultured supernatant at 10°C by two column chromatographies. About 20 mg of purified almelysin was obtained from 18.4 liters of the culture supernatant. The molecular mass of almelysin was estimated to be 28 kDa by SDS–PAGE and the isoelectric point was 4.3. The optimum pH for activity of almelysin was pH 8.5–9.0 and 6.5 using casein and (7-methoxycoumarin-4-yl)acetyl(MOCAc)-Pro-Leu-Gly-Leu-(N³-2,4-dinitrophenyl]-L-2,3-di-aminopropionyl)A₂pr(Dnp)]-Ala-Arg-NH₂ as substrates, respectively. Almelysin was stable between pH 7.5–8.0 and below 40°C. The optimum temperature for the activity was observed to be 40°C using both casein and MOCAc-Pro-Leu-Gly-Leu-A₂pr(Dnp)-Ala-Arg-NH₂ as substrates. The activity of almelysin was inhibited by such metallo chelators as EDTA and o-phenanthroline, while talopeptin, phosphoramidon, and SMPI, typical metalloproteinase inhibitors, had no effect. Almelysin primarily cleaved the Ala¹⁴-Leu¹⁵ bond and Phe²⁴-Phe²⁵ bond, and secondarily the Tyr¹⁶-Leu¹⁷ bond in oxidized insulin B-chain. However, almelysin could not cleave the His⁵-Leu⁶, His¹⁰-Leu¹¹, and Gly²³-Phe²⁴ bonds, which were cleaved by other metalloproteinases. These results indicate that the substrate specificity of almelysin is different from other metalloproteinases. Interestingly, Alteromonas sp. No. 3696 strain produced another proteinase as well as almelysin at 25°C.