Thioesterase variants having improved activity for the production of medium-chain fatty acid derivatives

A method for producing a medium-chain fatty acid derivative, the method comprising culturing a recombinant host cell comprising an engineered thioesterase variant in the presence of a carbon source under conditions suitable for the production of the medium-chain fatty acid derivative,

• wherein the engineered thioesterase variant has an amino acid sequence that has at least 90% sequence identity to SEQ ID NO:1 when the sequences are optimally aligned for maximum correspondence and compared over a comparison window, and has at least one substitution mutation at an amino acid position corresponding to position 3, 4, 6, 14, 15, 17, 22, 23, 37, 44, 45, 50, 54, 56, 64, 67, 91, 93, 110, 111, 114, 129, 132, 137, 158, 162, 165, 176, 178, 179, 185, 186, 196, 197, 198, 203, 210, 213, 217, 225, 227, 236, 240, 244, 245, 248, 254, 256, 258, 266, 278, 282, 292, 293, 294, 297, 298, 299, 300, 301, 302, 316, 321, 322, 325, or 328;
• and
• wherein the engineered thioesterase variant has improved activity for production of medium-chain fatty acid derivatives as compared to an enzyme having SEQ ID NO:
• 1.