Related Experiment Video
Updated: Jul 19, 2026

Electron Cryotomography of Bacterial Cells
Published on: May 6, 2010
Holo- and apo-cystalysin from Treponema denticola: two different conformations
Barbara Cellini1, Riccardo Montioli, Alessandra Bossi
1Dipartimento di Scienze Morfologico-Biomediche, Sezione di Chimica Biologica, Facoltà di Medicina e Chirurgia, Strada Le Grazie 8, Universita di Verona, 37134 Verona, Italy.
Abstract:
Cystalysin, the key virulence factor in the bacterium Treponema denticola responsible for periodontis, is a pyridoxal 5'-phosphate (PLP) enzyme which catalyzes, in addition to alpha,beta-elimination of L-cysteine, racemization and transamination of both enantiomers of alanine. In this paper several indicators have been used as probes of the different conformational status of T. denticola cystalysin in the holo and apo form. Compared to holoenzyme, the apoenzyme displays an altered reactivity of cysteine residues, a significantly different pI, and a differential susceptibility to proteinase K. The site of cleavage that is accessible in apocystalysin and masked in holocystalysin has been identified by mass spectrometry as the peptide bond between Phe 360 and Gly 361. This cleavage results in the loss of the C-terminal fragment corresponding to a molecular mass of 4289.21+/-0.1Da. The major fragment of cleaved enzyme retains its dimeric structure, binds the coenzyme with an affinity approximately 5000-fold lower than that of uncleaved holoenzyme, and in the reconstituted form is able to form the external aldimine with substrates. Although the break causes the loss of lyase, racemase and transaminase activities of D-alanine, it does not abolish the transaminase activity of L-alanine. Possible mechanistic and physiological implications are proposed.
Related Concept Videos
Conformations of Cyclohexane
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
Newman Projections
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as conformers.
Stereoisomerism of Cyclic Compounds
Bacterial Phylum Spirochaetes
Conformations of Ethane and Propane
Staggered conformation is a low energy and more stable conformation with the C-H bonds on the front carbon placed at 60°dihedral angles relative to the C-H bonds on the back carbon, leading to a reduced torsional strain. In staggered ethane, the...
Chair Conformation of Cyclohexane
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...

