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Cell Biology International (2006) 30, 56–65 (Printed in Great Britain)

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Evidence that collagen and tendon have monolayer water coverage in the native state

Gary D. Fullerton^* and Maxwell R. Amurao

Radiology Department, University of Texas Health Science Center at San Antonio, San Antonio, Floyd Curl Drive, TX 78229-3900, USA

Abstract

This paper investigates an alternative explanation for widely reported paradoxical intracellular water properties. The most frequent biological explanation assumes water structure extending multiple layers from surfaces of compactly folded macromolecules to explain large amounts of perturbed water. Long range water structuring, however, contradicts molecular models widely accepted by the scientific majority. This study questions whether the paradoxical cell water could result from larger than expected amounts of first layer interfacial water on internal protein surfaces rather than structured multilayers. Native mammalian tendon is selected for the study because (1) the organ consists of highly compact structures of a single macromolecular protein – collagen, (2) molecular structure and geometry of collagen is well characterized by X-ray diffraction, (3) molecular structure extends to the macroscopic tendon level and (4) perturbed water behavior similar to cellular water is reported on tendon. Native tendon holds 1.6gwater/gdrymass. The 62% native water content simulates the water content of many cell types. MicroCT studies of tendon dilatometry as a function of hydration are measured and correlated to X-ray diffraction measurements of interaxial separation. Correlations show that native tendon has sufficient water for only a single monolayer of interfacial water. Thus the paradoxical properties of water in native tendon are first-layer interfacial water properties. Similar water behavior on globular proteins suggests that paradoxical cell water behavior could be caused by larger than expected amounts of first layer interfacial water on internal and external macromolecular surfaces of cell components.

Key words: Collagen, Tendon, Cell hydration, Cell water content, Dilatometry, Intracellular water, Paradoxical cell water, Water structuring, Protein hydration.

^*Corresponding author.

Received 30 May 2005; accepted 30 September 2005