The secretory pathway of Pichia pastoris was genetically re-engineered to perform sequential glycosylation reactions that mimic early processing of N-glycans in humans and other higher mammals. After eliminating nonhuman glycosylation by deleting the initiating α-1,6-mannosyltransferase gene from P. pastoris, several combinatorial genetic libraries were constructed to localize active α-1,2-mannosidase and human β-1,2-N-acetylglucosaminyltransferase I (GnTI) in the secretory pathway. First, >32 N-terminal leader sequences of fungal type II membrane proteins were cloned to generate a leader library. Two additional libraries encoding catalytic domains of α-1,2-mannosidases and GnTI from mammals, insects, amphibians, worms, and fungi were cloned to generate catalytic domain libraries. In-frame fusions of the respective leader and catalytic domain libraries resulted in several hundred chimeric fusions of fungal targeting domains and catalytic domains. Although the majority of strains transformed with the mannosidase/leader library displayed only modest in vivo [i.e., low levels of mannose (Man)5-(GlcNAc)2] activity, we were able to isolate several yeast strains that produce almost homogenous N-glycans of the (Man)5-(GlcNAc)2 type. Transformation of these strains with a UDP-GlcNAc transporter and screening of a GnTI leader fusion library allowed for the isolation of strains that produce GlcNAc-(Man)5-(GlcNAc)2 in high yield. Recombinant expression of a human reporter protein in these engineered strains led to the formation of a glycoprotein with GlcNAc-(Man)5-(GlcNAc)2 as the primary N-glycan. Here we report a yeast able to synthesize hybrid glycans in high yield and open the door for engineering yeast to perform complex human-like glycosylation

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2D-NMR experiments are becoming more commonplace for organic analysis and promise to become as routine for chemists of this decade as 1D-NMR experiments were for chemists of the 1970's. However, undergraduate students seldom if ever are exposed to such experiments despite the increasing availability of high-field, superconducting magnets, more powerful computers, and menu driven software that is extremely friendly. This article outlines an experiment that integrates NMR into the organic teaching laboratory in a way designed to highlight the power of the technique and not merely to confirm the identity of known substances.

Our laboratory has focused on the re-engineered of the secretory pathway of Pichia pastoris to perform glycosylation reactions that mimic processing of N-glycans in humans and other higher mammals (1,2). A reporter protein with a single N-linked glycosylation site, a His-tagged Kringle 3 domain of human plasminogen (K3), was used to identify combinations of optimal leader/catalytic domain(s) to recreate human N-glycan processing in the Pichia system. In this chapter we describe detailed protocols for high-throughput purification of K3, enzymatic release of N-glycans, matrix-assisted laser desorption ionization time-of-flight and high-performance liquid chromatography analysis of the released N-glycans. The developed protocols can be adapted to the characterization of N-glycans from any purified protein expressed in P. pastoris.

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