Co-chaperone required during spermatogenesis to repress transposable elements and prevent their mobilization, which is essential for the germline integrity. Acts via the piRNA metabolic process, which mediates the repression of transposable elements during meiosis by forming complexes composed of piRNAs and Piwi proteins and govern the methylation and subsequent repression of transposons. Acts as a co-chaperone via its interaction with HSP90 and is required for the piRNA amplification process, the secondary piRNA biogenesis. May be required together with HSP90 in removal of 16 nucleotide ping-pong by-products from Piwi complexes, possibly facilitating turnover of Piwi complexes (By similarity). Interacts (via TPR repeats) with HSP90 (By similarity). Interacts with HSP72/HSPA2 and CLTC. Interacts with GAPDH; leading to inhibit GAPDH catalytic activity. Does not localize to pi-bodies. Localizes to meiotic chromosome cores and regions of homologous chromosome synapsis (By similarity). Detected in all tissues examined, with higher expression in testis, heart, skeletal muscle, liver, and kidney. FKBP6 is located in the Williams-Beuren syndrome (WBS) critical region. WBS results from a hemizygous deletion of several genes on chromosome 7q11.23, thought to arise as a consequence of unequal crossing over between highly homologous low-copy repeat sequences flanking the deleted region. Haploinsufficiency of FKBP6 may be the cause of certain cardiovascular and musculo-skeletal abnormalities observed in the disease (PubMed:9782077). A father and son with Williams-Beuren syndrome appear to have a common heterozygous deletion that includes FKBP6 gene. However, the haploinsufficiency for FKBP6 does not appear to preclude male fertility (PubMed:15770126). Defects in FKBP6 may be a cause of azoospermia. A study based on 323 patients with azoospermia or severe oligozoospermia suggested an association between FKBP6 variants and azoospermia (PubMed:17307919). However, other studies suggest that defects in FKBP6 are not a common cause of non-obstructive azoospermia (PubMed:16227348). Belongs to the FKBP6 family. Although it contains a PPIase FKBP-type domain, does not show peptidyl-prolyl cis-trans isomerase activity.