**5. Conclusions**

The fact that chondroitin synthase KfoC could polymerize a GalNAc-free polysaccharide certainly is the most striking result in the present study. The very low molecular weight of the new polysaccharide specie we called chondbiuronan is quite an advantage for chemical coupling and possible use in material coating or drug delivery due to its chondroitin-like structural features and because it could be slowly eliminated by GAG degrading enzymes. The use of lactose derivatives carrying chemical groups such as propargyl, allyl, and furyl groups should be possible as it has been shown that those precursors could be efficiently taken up to produce GAG derivatives in vivo allowing conjugation by click-chemistry [14,28].

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2218-273X/10/12/1667/s1, Figure S1: HSQC spectra of chondbiuronan (A) and chondroitin (B) obtained using 2% arabinose induction. Inset: chemical structure of the polysaccharides, Figure S2: HSQC spectrum of chondbiuronan showing the presence of Glc and GlcNAc incorporated in the polymer. Inset: chemical structure of the polysaccharides, Figure S3: COSY spectra of chondbiuronan (A) and chondroitin (B) obtained using 2% arabinose induction. Inset: chemical structure of the polysaccharides, Table S1: Genes, plasmids and *E. coli* strains used in this study.

**Author Contributions:** Conceptualization, M.L. and B.P.; strains, M.L. and B.P.; cultures and product extraction, M.L. and J.M.; SEC-MALS analyses, E.B.; NMR analyses, S.D.; enzymatic analyses, S.A.; original draft preparation, B.P.; supervision, B.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by a CIFRE fellowship from ANRT (Association Nationale de la Recherche et de la Technologie), grant number 2016/0814; Labex ARCANE and CBH-EUR-GS (ANR-17-EURE-0003), Glyco@Alps (ANR-15-IDEX-02), and PolyNat Carnot Institut (ANR-16-CARN-0025-01).

**Acknowledgments:** We acknowledge Laure Fort from ICMG (FR 2607) for mass spectrometry analyses and the NMR platform for its technical support.

**Conflicts of Interest:** The authors declare no conflict of interest.
