Screening and Identification of Aptamers Against Pulmonary Surfactant Protein A

Aptamers against surfactant protein A (SP-A) were selected by systematic evolution of ligands by exponential enrichment (SELEX) process from random-sequence nucleic acid library. Through the optimization of symmetric polymerase chain reaction (PCR) and asymmetric PCR parameters including amplification cycle number, annealing temperature and ratio of primers, a suitable screening system was established. We determined that the optimal cycle number was 12, the optimal annealing temperature was 55 °C, and the optimal ratio of primers was 80:1. The structure of aptamers was analyzed by DNAMAN software after being cloned and sequenced. After 9 rounds selection, the binding rate of ssDNA to SP-A increased from 1.3% to 33%. The aptamer AP-3 and AP-2 had the same conserved sequence TAC-GT; the aptamer AP-3 and AP-1 had the same sequence ACAG. The three-dimensional conformation of the aptamers was characterized by stem-loop structure.