Updated project metadata. The perinuclear theca (PT) is a highly condensed, largely insoluble protein structure that surrounds the nucleus of eutherian spermatozoa. While this structure is known to be important for fertilization, little is known regarding its proteomic composition. Recent reports have indicated that the PT unexpectedly houses several somatic proteins, such as core histones, which may be important post-fertilization during re-modelling of the male pronucleus. To explore the proteomic composition of the PT we performed the first in depth, label-free proteomic characterization of the PT of boar spermatozoa. To do this, a unique subcellular fractionation protocol was first performed to isolate the PT and increase our ability to detect lowly abundant sperm proteins. Through the use of this subcellular fractionation technique we were able to quantify 1802 proteins, a result that represents unparalleled depth of coverage for the boar sperm proteome and exceeds the entire known proteome of the Sus scrofa species so far. In the PT structure itself we identified 813 proteins and confirmed the presence of previously characterized PT proteins including the core histones H2A, H2B, H3 and H4, as well as Ras-related protein Rab-2A (RAB2A) and Rab-2B (RAB2B) amongst other RAB proteins. In addition to these previously characterized PT proteins, our data also revealed that the PT is replete in proteins critical for sperm-egg fusion including: Izumo sperm-egg fusion proteins 1-4 (IZUMO1-4) and phosphoinositide phospholipase C (PLCZ1).