Biochemistry (Moscow)

, Volume 74, Issue 10, pp 1088–1095 | Cite as

Compact acid-induced state of Clitoria ternatea agglutinin retains its biological activity

  • A. Naeem
  • M. Saleemuddin
  • R. H. KhanEmail author


The effects of pH on Clitoria ternatea agglutinin (CTA) were studied by spectroscopy, size-exclusion chromatography, and by measuring carbohydrate specificity. At pH 2.6, CTA lacks well-defined tertiary structure, as seen by fluorescence and near-UV CD spectra. Far-UV CD spectra show retention of 50% native-like secondary structure. The mean residue ellipticity at 217 nm plotted against pH showed a transition around pH 4.0 with loss of secondary structure leading to the formation of an acid-unfolded state. This state is relatively less denatured than the state induced by 6 M guanidine hydrochloride. With a further decrease in pH, this unfolded state regains ∼75% secondary structure at pH 1.2, leading to the formation of the A-state with native-like near-UV CD spectral features. Enhanced 8-anilino-1-naphthalene-sulfonate binding was observed in A-state, indicating a “molten-globule” like conformation with exposed hydrophobic residues. Acrylamide quenching data exhibit reduced accessibility of quencher to tryptophan, suggesting a compact conformation at low pH. Size-exclusion chromatography shows the presence of a compact intermediate with hydrodynamic size corresponding to a monomer. Thermal denaturation of the native state was cooperative single-step transition and of the A-state was non-cooperative two-step transition. A-State regains 72% of the carbohydrate-binding activity.

Key words

acid-induced unfolding Clitoria ternatea agglutinin carbohydrate binding molten-globule state thermal stability 



8-anilino-1-naphthalene-sulfonic acid


acid induced state


Clitoria ternatea agglutinin


guanidine hydrochloride


mean residue ellipticity


size-exclusion chromatography


acid unfolded state


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Copyright information

© Pleiades Publishing, Ltd. 2009

Authors and Affiliations

  1. 1.Interdisciplinary Biotechnology UnitAligarh Muslim UniversityAligarhIndia
  2. 2.Department of Biochemistry, Life ScienceAMUAligarhIndia

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