title: Nucleic acid aptamers as stabilizers of proteins: the stability of tetanus toxoid.
abstract: OBJECTIVE
  Exposure of tetanus toxoid to moisture leads to its aggregation and reduction of potency. The aim of this work was to use SELEX (systematic evolution of ligands by exponential enrichment) protocol and select aptamers which recognize tetanus toxoid (Mr ~150 kDa) with high affinity.
  
  
  METHODS
  Colyophilized preparations of tetanus toxoid and specific aptamers were encapsulated in PLGA microspheres and sustained release of the antigen was observed up to 55 days using different techniques.
  
  
  RESULTS
  The total protein released was between 40-55% (24-45% residual antigenicity) in the presence of the aptamers as compared to 25% (11% residual antigenicity) for the antigen alone. We show that instead of inhibiting absorption of moisture, the aptamers blocked the protein unfolding upon absorption of moisture, inhibiting the initiation of aggregation. When exposed to accelerated storage conditions, some of the RNA sequences were able to inhibit moisture-induced aggregation in vitro and retain antigenicity of tetanus toxoid.
  
  
  CONCLUSIONS
  Nucleic acid aptamers represent a novel class of protein stabilizers which stabilize the protein by interacting directly with it. This mechanism is unlike that of small molecules which alter the medium properties and hence depend on the stress condition a protein is exposed to.
authors.affiliation: Department of Biotechnology, National Institute of Pharmaceutical Education & Research-NIPER, Sector 67, SAS, Nagar, Punjab 160062, India.
authors.forename: Nishant Kumar
authors.initials: NK
authors.lastname: Jain
authors.forename: Hardik C
authors.initials: HC
authors.lastname: Jetani
authors.forename: Ipsita
authors.initials: I
authors.lastname: Roy
mesh_terms: D052157:Aptamers, Nucleotide / Q000737:chemistry*; D001483:Base Sequence; D003692:Delayed-Action Preparations / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D055550:Protein Stability; D058767:Protein Unfolding; D013745:Tetanus Toxoid / Q000008:administration & dosage* / Q000737:chemistry
chemical_list: D052157:Aptamers, Nucleotide; D003692:Delayed-Action Preparations; D013745:Tetanus Toxoid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid