Syn/anti lateral protonation

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• Author: ^^^Wim Nerinckx^^^
• Responsible Curator: ^^^Spencer Williams^^^

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Overview

This page provides a table on the spatial positioning of the catalytic general acid residue in the active sites of glycoside hydrolases. The table below updates those found in the seminal paper on this concept by Heightman and Vasella [1], and a following paper by Nerinckx et al. [2].

Background

The "not from above, but from the side" concept of semi-lateral glycosidic oxygen protonation by glycoside hydrolases was introduced by Heightman and Vasella [1]. It was originally only described for beta-equatorial glycoside hydrolases, but appears to be equally applicable to enzymes acting on an alpha-axial glycosidic bond [2]. When dividing subsite -1 into half-spaces by the Ox, C1' and H1' plane of the –1 glycoside, many ligand-complexed structures show that the proton donor is positioned either in the syn half-space, near the ring-oxygen of the –1 glycoside, or in the anti half-space at the opposite side of the ring-oxygen. Members of the same GH family are always syn or always anti protonators and this specificity appears to be preserved within clans of families. This page's compilation of subsite -1 occupied complexes shows that about 70% of all GH families are anti protonators.

Closer inspection of –1/+1 subsite-spanning ligands in crystal structures reveals a further intriguing corollary [2], [3]. In anti protonating GH enzymes, the scissile anomeric bond (often as thio-analogue) always shows a dihedral angle φ (O5'-C1'-[O,S]x-Cx) that is in the lowest- energy synclinal (gauche) position. A minus synclinal dihedral angle φ for an equatorial glycosidic bond, or plus synclinal for an axial bond [4], allows for hyperconjugative overlap of the C1'-O5' antibonding orbital with an antiperiplanar-oriented lone pair orbital lobe of the glycosidic oxygen, thereby creating partial double bond character and stabilization of the glycosidic bond by 4–5 kcal/mol; this ground-state stabilizing phenomenon is known as the ‘exo-anomeric effect’ [5] [6]. However, anti protonation occurs precisely on the oxygen’s antiperiplanar lone pair, which removes the stabilizing effect, thus providing an additional enzyme-strategy for lowering the activation barrier en route to the transition state (Figure 1 centre).

Syn protonators show a different strategy [2], [3]. In many –1/+1 subsite-spanning ligand complexes the dihedral angle φ of the scissile bond has been substantially twisted away from its lowest-energy synclinal position: clockwise to minus-anticlinal or antiperiplanar for beta-equatorial; counterclockwise to plus-anticlinal or antiperiplanar for alpha-axial anomeric bonds. This removes the hyperconjugative overlap and thus the stabilizing exo-anomeric effect. And because of this twisting, the lone pair of the glycosidic oxygen is pointing into the syn half- space, ready to be protonated by the syn-positioned proton donor (Figure 1 right).

Figure 1. Newman projections, with the glycosidic oxygen as proximal atom and the anomeric carbon as distal atom, showing anti (centre) versus syn (right) semi-lateral protonation in beta-equatorial (top) and alpha-axial (bottom) glycoside hydrolases. The indicated φ is the dihedral angle for O5'-C1'-O4-C4.

Table of syn/anti protonation examples

Note

This table contains only one example per GH family of a ligand-complexed protein structure where the syn positioning or anti positioning of the proton donor can be clearly observed; other examples may be available on a family-by-family basis. The reader is thus advised to consult the CAZy database for a current, comprehensive list of CAZyme structures. Where available, the selected examples are Michaelis-type complexes with the ligand spanning the -1/+1 subsites, since these have an intact glycosidic or thioglycosidic bond, or are N-analogs of the substrate (e.g. acarbose). In some examples, the proton donor has been mutated (e.g., to the corresponding amide or to an alanine), and in those cases one may wish to look at a superposition of the given PDB example with the structure of the native enzyme. If a Michaelis-type complex is not yet available, the second and third example choices, respectively, are trapped glycosyl-enzyme intermediates and product complexes where subsite -1 is correctly occupied.

Please also be aware that this is a large table with many data, so some (hopefully few) errors may have sneaked in. Please contact the page Author or Responsible Curator with corrections.

Table

This table can be re-sorted by clicking on the icons in the header (javascript must be turned on in your browser). To reset the page to be sorted by GH family, click the page tab at the very top of the page.

Family	Clan	Structure fold	Anomeric specificity	Mechanism	Syn/anti protonator	Example PDB ID	Enzyme	Organism	Ligand	General acid	Nucleophile or General base	Reference
GH1	A	(β/α)8	beta	retaining	anti	2cer	β-glycosidase S	Sulfolobus solfataricus P2	phenethyl glucoimidazol	Glu206	Glu387	[7]
GH2	A	(β/α)8	beta	retaining	anti	2vzu	exo-β-glucosaminidase	Amicolatopsis orientalis	PNP-β-d-glucosamine	Glu469	Glu541	[8]
GH3	none	(β/α)8	beta	retaining	anti	1iex	exo-1,3-1,4-glucanase	Hordeum vulgare	thiocellobiose	Glu491	Asp285	[9]
GH5	A	(β/α)8	beta	retaining	anti	1h2j	endo-β-1,4-glucanase	Bacillus agaradhaerens	2',4'-DNP-2-F-cellobioside	Glu129	Glu228	[10]
GH6	none	(β/α)8	beta	inverting	syn	1qjw	cellobiohydrolase 2	Hypocrea jecorina	(Glc)2-S-(Glc)2	Asp221	debated	[11]
GH7	B	β-jelly roll	beta	retaining	syn	1ovw	endo-1,4-glucanase	Fusarium oxysporum	thio-(Glc)5	Glu202	Glu197	[12]
GH8	M	(α/α)6	beta	inverting	anti	1kwf	endo-1,4-glucanase	Clostridium thermocellum	cellopentaose	Glu95	Asp278	[13]
GH9	none	(α/α)6	beta	inverting	syn	1rq5	cellobiohydrolase	Clostridium thermocellum	cellotetraose	Glu795	Asp383	[14]
GH10	A	(β/α)8	beta	retaining	anti	2d24	β-1,4-xylanase	Streptomyces olivaceoviridis E-86	xylopentaose	Glu128	Glu236	[15]
GH11	C	β-jelly roll	beta	retaining	syn	1bvv	xylanase	Bacillus circulans	Xyl-2-F-xylosyl	Glu172	Glu78	[16]
GH12	C	β-jelly roll	beta	retaining	syn	1w2u	endoglucanase	Humicola grisea	thiocellotetraose	Glu205	Glu120	[17]
GH13	H	(β/α)8	alpha	retaining	anti	1cxk	β-cyclodextrin glucanotransferase	Bacillus circulans	maltononaose	Glu257	Asp229	[18]
GH14	none	(β/α)8	alpha	inverting	syn	1itc	β-amylase	Bacillus cereus	maltopentaose	Glu172	Glu367	[19]
GH15	L	(α/α)6	alpha	inverting	syn	1gah	glucoamylase	Aspergillus awamori	acarbose	Glu179	Glu400	[20]
GH16	B	β-jelly roll	beta	retaining	syn	1urx	β-agarase A	Zobellia galactanivorans	oligoagarose	Glu152	Glu147	[21]
GH17	A	(β/α)8	beta	retaining	predicted anti by clan	see e.g. at GH1
GH18	K	(β/α)8	beta	retaining	anti	1ffr	chitinase A	Serratia marcescens	(NAG)6	Glu315	internal	[22]
GH20	K	(β/α)8	beta	retaining	anti	1c7s	chitobiase	Serratia marcescens	chitobiose	Glu540	internal	[23]
GH22	none	lysozyme type	beta	retaining	syn	1h6m	lysozyme C	Gallus gallus	Chit-2-F-chitosyl	Glu35	Asp52	[24]
GH23	none	lysozyme type	beta	inverting	syn	1lsp	lysozyme G	Cygnus atratus	Bulgecin A	Glu73	internal	[25]
GH24	I	α + β	beta	inverting	syn	148l	lysozyme E	Bacteriophage T4	chitobiosyl	Glu11	Glu26	[26]
GH26	A	(β/α)8	beta	retaining	anti	1gw1	mannanase A	Cellvibrio japonicus	2',4'-DNP-2-F-cellotrioside	Glu212	Glu320	[27]
GH27	D	(β/α)8	alpha	retaining	anti	1ktc	α-N-acetyl galactosaminidase	Gallus gallus	NAGal	Asp201	Asp410	[28]
GH28	N	β-helix	alpha	inverting	anti	2uvf	exo-polygalacturonosidase	Yersinia enterocolitica ATCC9610D	digalacturonic acid	Asp402	Asp381 Asp403	[29]
GH29	none	(β/α)8	alpha	retaining	syn	1hl9	α-l-fucosidase	Thermotoga maritima	2-F-fuco- pyranosyl	Glu266	Asp224	[30]
GH30	A	(β/α)8	beta	retaining	anti	2v3d	glucocerebrosidase 1	Homo sapiens	N-butyl-deoxynojirimycin	Glu235	Glu340	[31]
GH31	D	(β/α)8	alpha	retaining	anti	2qmj	maltase-glucoamylase	Homo sapiens	acarbose	Asp542	Asp443	[32]
GH32	J	5-fold β-propeller	beta	retaining	anti	2add	fructan β-(2,1)-fructosidase	Cichorium intybus	sucrose	Glu201	Asp22	[33]
GH33	E	6-fold β-propeller	alpha	retaining	anti	1s0i	trans-sialidase	Trypanosoma cruzi	sialyl-lactose	Asp59	Tyr342	[34]
GH34	E	6-fold β-propeller	alpha	retaining	anti	2bat	neuraminidase	Influenza A virus	sialic acid	Asp151	Tyr406	[35]
GH35	A	(β/α)8	beta	retaining	anti	1xc6	β-galactosidase	Penicillium sp.	d-galactose	Glu200	Glu299	[36]
GH37	G	(α/α)6	alpha	inverting	anti	2jf4	trehalase	Escherechia coli	validoxylamine	Asp312	Glu496	[37]
GH38	none	(β/α)7	alpha	retaining	anti	1qwn	α-mannosidase II	Drosophila melanogaster	5-F-β-l-gulosyl	Asp341	Asp204	[38]
GH39	A	(β/α)8	beta	retaining	anti	1uhv	β-xylosidase	Thermoanaerobacterium saccharolyticum	2-F-xylosyl	Glu160	Glu277	[39]
GH42	A	(β/α)8	beta	retaining	anti	1kwk	β-galactosidase	Thermus thermophylus A4	d-galactose	Glu141	Glu312	[40]
GH44	none	(β/α)8	beta	retaining	anti	2eqd	endoglucanase	Clostridium thermocellum	cellooctaose	Glu186	Glu359	[41]
GH45	none	6-strand. β-barrel	beta	inverting	syn	4eng	endo-1,4-glucanase	Humicola insolens	cellohexaose	Asp121	Asp10	[42]
GH46	I	α + β	beta	inverting	predicted syn by clan	see at GH24
GH47	none	(α/α)7	alpha	inverting	anti	1x9d	α-mannosidase I	Homo sapiens	Me-2-S-(α-Man)-2-thio-α-Man	Asp463	Glu599	[43], [44]
GH48	M	(α/α)6	beta	inverting	predicted anti by clan	see at GH8
GH49	N	β-helix	alpha	inverting	predicted anti by clan	see at GH28
GH50	A	(β/α)8	beta	retaining	predicted anti by clan	see e.g. at GH1
GH51	A	(β/α)8	alpha	retaining	anti	1qw9	α-l-arabino- furanosidase	Geobacillus stearothermophilus	PNP-l-arabino-furanoside	Glu175	Glu294	[45]
GH53	A	(β/α)8	beta	retaining	predicted anti by clan	see e.g. at GH1
GH54	none	β-sandwich	alpha	retaining	anti	1wd4	α-l-arabino- furanosidase B	Aspergillus kawachii	l-arabinofuranose	Asp297	Glu221	[46]
GH55	none	β-helix	beta	inverting	anti	3eqo	β-1,3-glucanase	Phanerochaete chrysosporium K-3	d-gluconolacton	Glu633	unknown	[47]
GH56	none	(β/α)7	beta	retaining	anti	1fcv	hyaluronidase	Apis mellifera	(hyaluron.)4	Glu113	internal	[48]
GH57	none	(β/α)7	alpha	retaining	anti	1kly	glucanotransferase	Thermococcus litoralis	acarbose	Asp214	Glu123	[49]
GH59	A	(β/α)8	beta	retaining	predicted anti by clan	see e.g. at GH1
GH63	G	(α/α)6	alpha	inverting	predicted anti by clan	see at GH37
GH65	L	(α/α)6	alpha	inverting	predicted syn by clan	see at GH15
GH67	none	(β/α)8	alpha	inverting	syn	1gql	α-glucuronidase	Cellvibrio japonicus Ueda107	d-glucuronic acid	Glu292	unknown	[50]
GH68	J	5-fold β-propeller	beta	retaining	anti	1pt2	levansucrase	Bacillus subtilis	sucrose	Glu342	Asp86	[51]
GH70	H	(β/α)8	alpha	retaining	predicted anti by clan	see e.g. at GH13
GH72	A	(β/α)8	beta	retaining	anti	2w62	β-1,3-glucano- transferase	Saccharomyces cerevisiae S288C	laminaripentaose	Glu176	Glu275	[52]
GH74	none	7-fold β-propeller	beta	inverting	syn	2ebs	cellobiohydrolase (OXG-RCBH)	Geotrichum sp. m128	xyloglucan heptasaccharide	Asp465	Asp35	[53]
GH77	H	(β/α)8	alpha	retaining	anti	1esw	amylomaltase	Thermus aquaticus	acarbose	Asp395	Asp293	[54]
GH79	A	(β/α)8	beta	retaining	predicted anti by clan	see e.g. at GH1
GH80	I	α + β	beta	inverting	predicted syn by clan	see at GH24
GH83	E	6-fold β-propeller	alpha	retaining	predicted anti by clan	see e.g. at GH33
GH84	none	(β/α)8	beta	retaining	anti	2chn	β-N-acetyl- glucosaminidase	Bacteroides thetaiota- omicron VPI-5482	NAG-thiazoline	Glu242	internal	[55]
GH85	K	(β/α)8	beta	retaining	anti	2w92	endo-β-N-acetyl- glucosaminidase D	Streptococcus pneumoniae TIGR4	NAG-thiazoline	Glu337	internal	[56]
GH86	A	(β/α)8	beta	retaining	predicted anti by clan	see e.g. at GH1
GH89	none	(β/α)8	alpha	retaining	anti	2vcb	α-N-acetyl- glucosaminidase	Clostridium perfringens	PUGNAc	Glu483	Glu601	[57]
GH92	none	(α/α)6 + β-sandw.	alpha	inverting	anti	2ww1	α-1,2-mannosidase	Bacteroides thetaiota- omicron VPI-5482	thiomannobioside	Glu533	Asp644 Asp642	[58]
GH93	E	6-fold β-propeller	alpha	retaining	predicted anti by clan	see e.g. at GH33
GH94	none	(α/α)6	beta	inverting	syn	1v7x	chitobiose phosphorylase	Vibrio proteolyticus	GlcNAc	Asp492	phosphate	[59]
GH95	none	(α/α)6	alpha	inverting	anti	2ead	α-1,2-l-fucosidase	Bifidobacterium bifidum	Fuc-α-1,2-Gal	Glu566	Asn423 Asp766	[60]
GH97	none	(β/α)8	alpha	retaining + inverting	anti	2zq0	α-glucosidase	Bacteroides thetaiota- omicron VPI-5482	acarbose	Glu532	Glu508	[61]
GH102	none	double-ψ β-barrel	beta	retaining	syn	2pi8	lytic transglycosylase A	Escherechia coli	chitohexaose	Asp308	none	[62]
GH113	A	(β/α)8	beta	retaining	predicted anti by clan	see e.g. at GH1

References

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