Part of a complex that catalyzes the reversible cleavage of acetyl-CoA, allowing autotrophic growth from CO(2). Probably maintains the overall quaternary structure of the ACDS complex. Heterodimer of delta and gamma chains. The ACDS complex is made up of alpha, epsilon, beta, gamma and delta chains with a probable stoichiometry of (alpha(2)epsilon(2))(4)-beta(8)-(gamma(1)delta(1))(8). Belongs to the CdhD family.