Could multiple low-affinity bonds mediate primary sperm-zona pellucida binding?

The current model for primary sperm binding to the zona pellucida is that a cell-surface sperm protein binds with high affinity in an order-specific manner to one of the zona pellucida proteins, ZP3. However, the molecular details of primary sperm-zona pellucida binding remain elusive. A possible revised model is that multiple low-affinity bonds between spermatozoa and the zona pellucida may be sufficient for primary binding. The avidity of several low-affinity bonds can exceed that of a single high-affinity bond, which is sufficient to tether a motile spermatozoon. A mechanism involving multiple low-affinity bonds could account for some of the difficulties in elucidating primary sperm-zona pellucida interactions.

ELECTRON MICROSCOPE STUDIES OF SPERMATOZOA OF RHYNCHOSCIARA SP

The flagellar complex of the unusual motile spermatozoon of the fungus gnat, Rhynchosciara sp, does not conform to the usual "9 + 2" filament pattern but rather consists of over 350 pairs of filaments (doublet microtubules) distributed in a spiral array. Experiments were designed to disrupt and extract flagellar microtubular components from spermatozoa of the fungus gnat. Pepsin, chymotrypsin, potassium iodide, urea, and heat were used to extract specific portions of microtubule walls Such experiments provide information on the composition of the wall and the existence of wall sites selectively sensitive to various treatments Results obtained include: (a) doublet microtubules are comprised at least in part of protein, and all subunits are probably not identical; (b) a portion of the B subfiber is apparently more sensitive to disruption than other portions of the doublet microtubule; and (c) the ac cessory singlet microtubules may be chemically different from the doublet microtubules