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Several post-translational protein modifications lie predominantly within regions of disorder: the biased localization has been proposed to expand the binding versatility of disordered regions. However, investigating a representative dataset of 500 human N-glycoproteins, we observed the sites of N-linked glycosylations or N-glycosites, to be predominantly present in the regions of predicted order. When compared with disordered stretches, ordered regions were not found to be enriched for asparagines, serines and threonines, residues that constitute the sequon signature for conjugation of N-glycans. We then investigated the basis of mutual exclusivity between disorder and N-glycosites on the basis of amino acid distribution: when compared with control ordered residue stretches without any N-glycosites, residue neighborhoods surrounding N-glycosites showed a depletion of bulky, hydrophobic and disorder-promoting amino acids and an enrichment for flexible and accessible residues that are frequently found in coiled structures. When compared with control disordered residue stretches without any N-glycosites, N-glycosite neighborhoods were depleted of charged, polar, hydrophobic and flexible residues and enriched for aromatic, accessible and order-promoting residues with a tendency to be part of coiled and β structures. N-glycosite neighborhoods also showed greater phylogenetic conservation among amniotes, compared with control ordered regions, which in turn were more conserved than disordered control regions. Our results lead us to propose that unique primary structural compositions and differential propensities for evolvability allowed for the mutual spatial exclusion of N-glycosite neighborhoods and disordered stretches.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Several post-translational modifications of proteins lie within regions of disorder, stretches of amino acid residues that exhibit a dynamic tertiary structure and resist crystallization. Such localization has been proposed to expand the binding versatility of the disordered regions, and hence, the repertoire of interacting partners for the proteins. However, investigating a dataset of 500 human N-linked glycoproteins, we observed that the sites of N-linked glycosylations, or N-glycosites, lay predominantly within the regions of predicted order rather than their unstructured counterparts. This mutual exclusivity between disordered stretches and N-glycosites could not be reconciled merely through asymmetry in distribution of asparagines, serines or threonines residues, which comprise the minimum-required signature for conjugation by N-linked glycans, but rather by a contextual enrichment of these residues next to each other within the ordered portions. In fact, N-glycosite neighborhoods and disordered stretches showed distinct sets of enriched residues suggesting their individualized roles in protein phenotype. N-glycosite neighborhood residues also showed higher phylogenetic conservation than disordered stretches within amniote orthologs of glycoproteins. However, a universal search for residue-combinations that are putatively domain-constitutive ranked the disordered regions higher than the N-glycosite neighborhoods. We propose that amino acid residue-combinations bias the permissivity for N-glycoconjugation within ordered regions, so as to balance the tradeoff between the evolution of protein stability, and function, contributed by the N-linked glycans and disordered regions respectively.

Epithelial ovarian cancer (EOC) is characterized by resistance to platinum-based therapy, resulting in rapid progression and poor survival. Here, we ask whether drug resistance and invasiveness coevolve to drive metastasis. Selection experiments involving pulsed carboplatin exposure established isogenic chemoresistant variants of lines, which typify high-grade serous ovarian carcinoma (HGSOC), the most aggressive type of EOC. Time-lapse imaging showed enhanced migration of resistant single cells and their collectives. Resistant cell spheroids spread faster on Collagen I substrata than sensitive controls. The resistant OVCAR-3 transcriptome was ontologically enriched for migration and showed overlap with previously reported markers of resistance in EOC patients and other evolved lines. Gene set enrichment predicted transition between epithelial, mesenchymal, and amoeboid states is higher in resistance compared to control lines. Lower matrix adhesion, weak focal adhesion, and highly deformable and translatory dynamics of cell collectives indicated that resistant cancer cells displayed a unique collective amoeboid-like migration. When injected intraperitoneally into immunodeficient mice, resistant cells colonized to a greater extent on parietal mucosae. Ex vivo, suspended resistant cells formed moruloids associated with quicker peritoneal adhesion, clearing human coelomic mesothelial monolayers with higher efficiency. Knockdown in resistant OVCAR-3 cells of two upregulated proteins, E-cadherin and LGALS3BP, had distinct consequences. E-cadherin knockdown partially restored sensitivity to carboplatin but did not affect invasion. In contrast, silencing LGALS3BP decreased invasion but not resistance. Our results suggest that drug resistance and invasiveness could coevolve through the upregulation of distinct trait drivers in EOC.