The Arabidopsis xylosyltransferases, XXT3, XXT4, and XXT5, are essential to complete the fully xylosylated glucan backbone XXXG-type structure of xyloglucans.

Although most xyloglucans (XyGs) biosynthesis enzymes have been identified, the molecular mechanism that defines XyG branching patterns is unclear. Four out of five XyG xylosyltransferases (XXT1, XXT2, XXT4, and XXT5) are known to add the xylosyl residue from UDP-xylose onto a glucan backbone chain; however, the function of XXT3 has yet to be demonstrated. Single xxt3 and triple xxt3xxt4xxt5 mutant Arabidopsis (Arabidopsis thaliana) plants were generated using CRISPR-Cas9 technology to determine the specific function of XXT3. Combined biochemical, bioinformatic, and morphological data conclusively established for the first time that XXT3, together with XXT4 and XXT5, adds xylosyl residue specifically at the third glucose in the glucan chain to synthesize XXXG-type XyGs. We propose that the specificity of XXT3, XXT4, and XXT5 is directed toward the prior synthesis of the acceptor substrate by the other two enzymes, XXT1 and XXT2. We also conclude that XXT5 plays a dominant role in the synthesis of XXXG-type XyGs, while XXT3 and XXT4 complementarily contribute their activities in a tissue-specific manner. The newly generated xxt3xxt4xxt5 mutant produces only XXGG-type XyGs, which further helps to understand the impact of structurally deficient polysaccharides on plant cell wall organization, growth, and development.

Xyloglucan Biosynthesis: From Genes to Proteins and Their Functions.

The plant's recalcitrant cell wall is composed of numerous polysaccharides, including cellulose, hemicellulose, and pectin. The most abundant hemicellulose in dicot cell walls is xyloglucan, which consists of a ß-(1- > 4) glucan backbone with α-(1- > 6) xylosylation producing an XXGG or XXXG pattern. Xylose residues of xyloglucan are branched further with different patterns of arabinose, fucose, galactose, and acetylation that varies between species. Although xyloglucan research in other species lag behind Arabidopsis thaliana, significant advances have been made into the agriculturally relevant species Oryza sativa and Solanum lycopersicum, which can be considered model organisms for XXGG type xyloglucan. In this review, we will present what is currently known about xyloglucan biosynthesis in A. thaliana, O. sativa, and S. lycopersicum and discuss the recent advances in the characterization of the glycosyltransferases involved in this complex process and their organization in the Golgi.

How to Effectively Decrease Patient Co-Payments of High-Cost Drugs Through Innovation: Lessons From the Karmanos Specialty Pharmacy.

PURPOSE: High-cost drugs impose a financial burden on patients with cancer. Karmanos Specialty Pharmacy (KSP) developed a process to automate financial assistance (FA) applications to decrease patient drug cost. We evaluate the outcomes of this program on cost to patients and payers. METHODS: This is an observational, retrospective study of the KSP claims data set from January to December 2019, accessed by 13 statewide cancer centers within Michigan. Drug cost of patients, payers, FA (funds to lower patient drug cost), and types of FA were obtained. A subset analysis was performed to determine drug delivery times. RESULTS: In 2019, 869 prescriptions and 1,722 prescription fills were provided to 463 patients through KSP. The total cost of drug claims was approximately $10 million US dollars (USD) among Medicare patients (58%), approximately $3.4 million USD for privately insured patients (20%), and approximately $3.7 million USD for Medicaid patients (22%). Twenty-seven percent of patients (22% of all prescription fills) required additional FA with initial total co-payment claims of $335,216 USD. $280,988 USD of FA was obtained, which substantially lowered total patient costs by 81%. $250,818 USD of FA obtained was from foundation grants (327 fills), and $21,441 USD from manufacturer co-pay cards (47 fills). An additional $12,260 USD (12 fills) from a Karmanos Patient Assistance Fund was used. There was high dependence on foundation grant assistance among Medicare patients (33% of claims). In a subset analysis, the median time from prescription written to delivery to the patient was < 7 days (0-56 days). CONCLUSION: Twenty-seven percent of patients (22% of prescriptions fills) in 2019 required additional FA for high-cost drugs. KSP substantially reduced patient cost by implementing an efficient process using additional pharmacy assistants to obtain FA.