AUTHOR=Bhatt Jay M. , Enriquez Adrian S. , Wang Jinliang , Rojo Humberto M. , Molugu Sudheer K. , Hildenbrand Zacariah L. , Bernal Ricardo A. TITLE=Single-Ring Intermediates Are Essential for Some Chaperonins JOURNAL=Frontiers in Molecular Biosciences VOLUME=5 YEAR=2018 URL=https://www.frontiersin.org/journals/molecular-biosciences/articles/10.3389/fmolb.2018.00042 DOI=10.3389/fmolb.2018.00042 ISSN=2296-889X ABSTRACT=

Chaperonins are macromolecular complexes found throughout all kingdoms of life that assist unfolded proteins reach a biologically active state. Historically, chaperonins have been classified into two groups based on sequence, subunit structure, and the requirement for a co-chaperonin. Here, we present a brief review of chaperonins that can form double- and single-ring conformational intermediates in their protein-folding catalytic pathway. To date, the bacteriophage encoded chaperonins ϕ-EL and OBP, human mitochondrial chaperonin and most recently, the bacterial groEL/ES systems, have been reported to form single-ring intermediates as part of their normal protein-folding activity. These double-ring chaperonins separate into single-ring intermediates that have the ability to independently fold a protein. We discuss the structural and functional features along with the biological relevance of single-ring intermediates in cellular protein folding. Of special interest are the ϕ-EL and OBP chaperonins which demonstrate features of both group I and II chaperonins in addition to their ability to function via single-ring intermediates.