Isolation and Sequence of a Novel Human Chondrocyte Protein Related to Mammalian Members of the Chitinase Protein Family

doi:10.1074/jbc.271.32.19415

Isolation and Sequence of a Novel Human Chondrocyte Protein Related to Mammalian Members of the Chitinase Protein Family*

From the Department of Biology, University of California, San Diego, La Jolla, California 92093

^‡ To whom correspondence should be addressed:
Dept. of Biology, 0322, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0322.
Tel.: 619-534-2120; Fax: 619-534-1492.

Abstract

We describe the isolation of a novel protein from the conditioned medium of human articular cartilage chondrocytes in primary culture. This 39-kDa protein has the N-terminal sequence YKL, which we have termed YKL-39. The 1434-nucleotide sequence of the YKL-39 cDNA predicts a 385-residue initial translation product and a 364-residue mature YKL-39. The amino acid sequence of YKL-39 is most closely related to YKL-40, followed by macrophage chitotriosidase, oviductal glycoprotein, and macrophage YM-1. All five proteins share significant sequence identity with bacterial chitinases and have the probable structure of an (αβ)₈ barrel. YKL-39 lacks the active site glutamate, which is essential for the activity of chitinases, and as expected has no chitinase activity. The highest level of YKL-39 mRNA expression is seen in chondrocytes, followed by synoviocytes, lung, and heart. YKL-39 accounts for 4% of the protein in chondrocyte-conditioned medium, prostromelysin accounts for 17%, and YKL-40 accounts for 33%. In contrast to YKL-40, YKL-39 is not a glycoprotein and does not bind to heparin.

Footnotes

↵* This work was supported in part by a grant from NovaDx, Inc. and by United States Public Health Service Grant AG07996. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) U49835[GenBank].
↵¹ The abbreviations used are:

DMEM

Dulbecco's modified Eagle's medium

YKL-39

the 39-kDa human chondrocyte protein with the N terminus YKL

YKL-40

the 40-kDa human chondrocyte protein with the N terminus YKL (also called HC gp-39; see Ref. 4)

PAGE

polyacrylamide gel electrophoresis.
↵² When purified YKL-40 is dried in preparation for loading onto a gel, it gives variable amounts of dimeric YKL-40 (data not shown). This accounts for the 80-kDa band seen in Fig. 1 (inset), a band that was not seen in the SDS-PAGE of these fractions when the drying step was omitted.
- Received April 3, 1996.
- Revision received May 20, 1996.