br accompanied and the unripe and ripe
accompanied, and the unripe and ripe status of each point was con-firmed. In this way, we can focus on studying whether the chelate-soluble pectin (CSF) only modified by the natural ripening (after fruit harvesting) and without any modification (by chemicals or pH or by ion-exchange chromatography) would differently affect cancer Suramin growth and galectin-3 binding.
Galectin-3 is a pro-metastatic lectin that is overexpressed in some cancer cell lines , including in early stages of colon cancer . Both in vivo and in vitro studies confirmed that increased galectin-3 expres-sion during cancer progression enhances tumor growth, invasiveness, and metastatic potential, as reviewed previously . The interaction of pectin with galectin-3 CRD prevents galectin-3–mediated effects such as the increase in cells migration and adhesion and the inhibition of cells apoptosis . Lactose is known to bind to the CRD of galectin-
3. Furthermore, pectin fragments that contain galactosides, such as arabinogalactan and galactan sidechains in the RGI regions, are also in-teresting candidates that could interact with the galectin-3 CRD domain . However, while neutral fragments can directly bind on galectin-3
CRD domain, galacturonans might not have a specific binding but in-stead have a nonspecific charge–charge interaction with galectin-3 . Another study focused on how RG and HG structures bind to galectin-3 suggests that RG and HG polysaccharides act in concert:
their combination in specific proportions enhances galectin-3 activity synergistically . It happens because HG interacts with RG promoting increased activity of RG binding to galectin-3, probably by exposing ad-ditional galectin-binding sites on the RG . In the present study, we showed that 3CSF was the only papaya chelate-pectin fraction that inhibited galectin-3–mediated hemagglutination. The 3CSF had similar GalA content and degree of esterification from those of other ripening-time points. However, 3CSF had a lower molecular weight peak, which suggests that this CSF is more functional and available to interact with galectin-3 CRD, even with less Gal content since the neutral ramifica-tions could have a molecular size that facilitate the interaction with galectin-3. Besides, the binding to galectin-3 could also occur through nonspecific charge–charge interaction with the smaller HG structures of 3CSF, as previously suggested . The comparisons between the AFM images of 3CSF and 1CSF reveal that samples from unripe papayas possess higher linear and branched structures and possess agglomer-ates. These branch structures visualized through AFM seemed to be formed by GalA residues and linked via a branched GalA residue . The 3CSF had smaller linear structures in lower amounts, and it was not possible to visualize the branched structures. The most abundant structures in 3CSF are molecules agglomerated with an oval shape. In the chelate-soluble fraction extracted from pears, the long and highly
Fig. 5. 3CSF structural determination by NMR spectroscopy. A) 1D 1H NMR spectrum. B) 13C\\1H HSQC spectrum. C) 13C\\1H HMBC spectrum. 3CSF: chelate-soluble fraction extracted from papaya with 3 days after harvest. D) Schematic representation of 3CSF methylated and non-methylated galacturonic acid structure. E) Predominant part of HG not methylated or methylated. F) 3CSF probable presence of RGI fractions enriched by galactans and arabinans.
branched structure is visible, and polygalacturonase action induces the formation of spot-like and oval shapes . During papaya ripening, an increase in the activity of polygalacturonases [21,46] may also be responsible for the formation of more agglomerates in 3CSF com-pared to 1 CSF. The FT-IR analysis also showed that peaks character-istics of neutral sugar was increased in 3CSF and it could be related not only to the amount of neutral substitution but also with the po-sition and the degree of substitution . To summarize, the