The hydrophobic behaviour of statherin is altered by pH and calcium

To explore how statherin's hydrophobic properties affects its binding behaviour.

Synthetized statherin with or without phosphorylation (Statherin (±p)) or calcium was incubated with defined hydrophobic and hydrophilic charged particles. Bound protein was eluted by TBST (tris buffered saline with tween 20) and EDTA buffers to break hydrophobic and hydrophilic interactions. Statherin (±p) diluted in different pH (3.0/4.2/7.0) were incubated with hydrophobic particles followed by TBST elution to study how pH affects its hydrophobic interaction. Film formation ability was assessed by resolubilizing any visible film at the air-liquid interface and quantifying by electrophoresis after leaving Statherin (±p) solutions in petri dishes for 30 mins. Statherin (±p) self-association behaviour with or without calcium was also assessed by transmission electron microscope (TEM) and particle size spectroscopy.

Greatest binding was seen for Statherin (+p) to hydrophobic particles which was decreased by 35% after adding calcium and increased by 30% by increasing solution acidity. On positively charged particles, binding was increased by 30% with calcium and uniquely was eluted by EDTA. Interestingly, only Statherin (+p) with calcium formed a visible film. Size detection showed that calcium induced large associations of Statherin (±p) and TEM revealed Statherin (+p) with calcium formed oval micelles (200 nm), while Statherin (-p) formed small round and rod micelles regardless of calcium.

This study demonstrates statherin's hydrophobic properties are affected by calcium and pH and dominates its physical properties. This may shed light on how statherin assembles in saliva which may affect its binding and remineralization ability with teeth.