Functional aspects of the human salivary cystatins in the oral environment.
OBJECTIVE
The aim of this study was to investigate the cysteine protease inhibitory properties of the human salivary cystatins S, SA and SN in order to identify potential in vivo target cysteine proteases which may include those involved in periodontal tissue destruction. In addition, the potential role of the salivary cystatins with respect to the tooth mineral balance and pellicle formation was also investigated.


METHODS
Salivary cystatins S major, S minor, SA, SAT (a truncated form of SA) and SN were purified from human submandibular sublingual saliva. Sensitive fluorometric assays were used to test the inhibitory action of each purified form of salivary cystatin against a variety of cysteine proteases and to determine whether pH affected their inhibitory activity towards the well-characterized cysteine protease papain. Their potential role in the mineral balance of the tooth was assessed by the measurement of calcium binding and the rate of binding to carbonated apatite (CAP).


CONCLUSIONS
Salivary cystatin SN was found to inhibit the human lysosomal cathepsins B, H and L and salivary cystatin SA was found to inhibit human lysosomal cathepsin L in vitro. These proteases are involved in periodontal tissue destruction and these data suggest that salivary cystatins SA and SN are involved in the control of the proteolytic events in vivo. Salivary cystatin S was not an inhibitor of the cysteine proteases tested suggesting that its primary role is not as a cysteine protease inhibitor. However, S was able to bind more calcium and bind more rapidly to CAP than SA or SN, suggesting that its primary role in the oral environment is likely to be the involvement with the mineral balance of the tooth.
Baron
A
A
Department of Restorative Dentistry, University of California, San Francisco, CA 94143, USA.
DeCarlo
A
A
Featherstone
J
J
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D015891:Cystatins / Q000737:chemistry / Q000502:physiology*; D015853:Cysteine Proteinase Inhibitors / Q000737:chemistry / Q000502:physiology*; D017886:Durapatite / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D008969:Molecular Sequence Data; D010510:Periodontal Diseases / Q000201:enzymology*; D011485:Protein Binding; D055333:Salivary Cystatins; D012471:Salivary Proteins and Peptides / Q000502:physiology*
C525171:CST1 protein, human; C525172:CST2 protein, human; C525173:CST4 protein, human; D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D055333:Salivary Cystatins; D012471:Salivary Proteins and Peptides; D017886:Durapatite; D002118:Calcium