Mitochondrial processing peptidase activity is controlled by the processing of alpha-MPP during development in Dictyostelium discoideum.

We investigated the expression of the alpha subunit of the Dictyostelium mitochondrial processing peptidase (Ddalpha-MPP) during development. Ddalpha-MPP mRNA is expressed at the highest levels in vegetatively growing cells and during early development, and is markedly downregulated after 10 h of development. The Ddalpha-MPP protein is expressed as two forms, designated alpha-MPP(H) and alpha-MPP(L), throughout the Dictyostelium life cycle. The larger form, alpha-MPP(H), is cleaved to produce the functional alpha-MPP(L) form. We were not able to isolate mutants in which the alpha-mpp gene had been disrupted. Instead, an antisense transformant, alphaA2, expressing alpha-MPP at a lower level than the wild-type AX-3 was isolated to examine the function of the alpha-MPP protein. Development of the alphaA2 strain was normal until the slug formation stage, but the slug stage was prolonged to approximately 24 h. In this prolonged slug stage, only alpha-MPP(H) was present, and alpha-MPP(L) protein and MPP activity were not detected. After 28 h, alpha-MPP(L) and MPP activity reappeared, and normal fruiting bodies were formed after a delay of approximately 8 h compared with normal development. These results indicate that MPP activity is controlled by the processing of alpha-MPP(H) to alpha-MPP(L) during development in Dictyostelium.

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