Controlled libraries, also known as site-directed unsaturation libraries or Trimer libraries, are a class of libraries similar to degenerate libraries. The difference is that the amino acid mutation point of the controlled library is replaced by some of the other 20 amino acids, not all 20. And the ratio of several amino acids to be replaced can be average, or it can be artificially controlled according to a specific ratio. The main purpose of the controlled library is to reduce the theoretical library capacity and remove some high-probability nonsense mutations, thereby reducing the later screening effort. Focus on the sequence of the mutants that are most likely to be obtained, so as to facilitate the in-depth study of mutations of a few amino acids. For example, in-depth study of the effect of a few amino acids around the catalytic site of the enzyme on the catalytic properties of the enzyme.

Controlled libraries are often implemented with Trimer primers. Unlike ordinary primers where the single nucleotides are synthesized one by one, Trimer primers are three nucleotides that are pre-linked into a nucleotide triplet, called Trimer. When synthesizing primers, just connect the corresponding Trimer at the required position. If you need several amino acids to appear at this position, just mix the Trimers of these amino acids and connect them. The ratio of each amino acid at this position in the finished library is controlled by controlling the ratio of each Trimer.

Controlled libraries