Towards Protein Engineering of Chlamydomonas Reinhardtii Chloroplast ATP Synthase

Abstract

Membrane bound ATP synthases from chloroplasts, mitochondria and bacteria are the major catalyst in the transduction of energy derived from electron transport, whereby the proton flow across a membrane energized by electron transport is the driving force for synthesis of ATP. The chloroplast ATP synthase (CF_O · CF₁) is one of four major protein complexes of the thylakoid membrane (1, 2). CF_O contains four subunits (I–IV) and CF₁ is composed of five different polypeptide chains designated α — ε in order of decreasing Mr (1). The genes encoding subunits α, β and e (atpA, atpB and atpE) of CF₁ are located in the chloroplast DNA, while the genes encoding subunits γ and δ (atpC and atpD) are located in the nuclear DNA. All genes encoding CF₁ subunits have been identified and their DNA sequences determined in at least one species. The molecular weight of CF₁ is about 380,000 and the subunit stoichiometry is α₃β₃γδε. An α₃β₃γ complex has been characterized and is a suitable model to study structure and function relationship of CF₁ (3). The α₃β₃ complex is the catalytic core of F-type ATPases (4, 5). The other subunits appear to be responsible for the binding of CF₁ to CF_O and the coupling of ATP synthesis to proton translocation. In CF₁, the y subunit regulates the enzyme activity according to the degree of energization of the membrane (6, 7). Active CF₁ complexes of spinach and maize have been reconstituted from isolated subunits (8).