Strongly interacts with EsxL to form a heterodimeric complex under reducing conditions. The complex is regulated by the redox state of EsxL. Probably secreted via the ESX-5 / type VII secretion system (T7SS). Differentially expressed under different growth conditions. Highly expressed in sputum bacteria. EsxKL deletion mutant shows reduced intracellular growth in primary human macrophages. Also shows growth defects in the absence of host cells. Belongs to the WXG100 family. CFP-10 subfamily.