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Neutralizing antibodies can prevent hepatitis C virus (HCV) infection, one of the leading causes of cirrhosis and liver cancer. Here, we characterized the immunoglobulin repertoire of memory B-cell antibodies against a linear epitope in the central front layer of the HCV envelope (E2; amino acids 483-499) in patients who were infected in a single-source outbreak. A reverse transcription polymerase chain reaction-based immunoglobulin gene cloning and recombinant expression approach was used to express monoclonal antibodies from HCV E2 peptide-binding immunoglobulin G-positive memory B cells. We identified highly mutated antibodies with a neutralizing effect in vitro against different genotype isolates sharing similar gene features. Our data confirm the importance of VH1-69 use for neutralizing activity. The data offer a promising basis for vaccine research and the use of anti-E2 antibodies as a means of passive immunization., (© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Plant type III polyketide synthases (PKSs) catalyze the condensation of malonyl-CoA units with various CoA ester starter molecules to generate a diverse array of natural products. The fatty acyl-CoA esters synthesized by Arabidopsis thaliana ACYL-COA SYNTHETASE5 (ACOS5) are key intermediates in the biosynthesis of sporopollenin, the major constituent of exine in the outer pollen wall. By coexpression analysis, we identified two Arabidopsis PKS genes, POLYKETIDE SYNTHASE A (PKSA) and PKSB (also known as LAP6 and LAP5, respectively) that are tightly coexpressed with ACOS5. Recombinant PKSA and PKSB proteins generated tri-and tetraketide α-pyrone compounds in vitro from a broad range of potential ACOS5-generated fatty acyl-CoA starter substrates by condensation with malonyl-CoA. Furthermore, substrate preference profile and kinetic analyses strongly suggested that in planta substrates for both enzymes are midchain- and ω-hydroxylated fatty acyl-CoAs (e.g., 12-hydroxyoctadecanoyl-CoA and 16-hydroxyhexadecanoyl-CoA), which are the products of sequential actions of anther-specific fatty acid hydroxylases and acyl-CoA synthetase. PKSA and PKSB are specifically and transiently expressed in tapetal cells during microspore development in Arabidopsis anthers. Mutants compromised in expression of the PKS genes displayed pollen exine layer defects, and a double pksa pksb mutant was completely male sterile, with no apparent exine. These results show that hydroxylated α-pyrone polyketide compounds generated by the sequential action of ACOS5 and PKSA/B are potential and previously unknown sporopollenin precursors.