Table 1.

Overview of available structures with AP4A as a protein ligand. A search was performed in October 2022 with the AP4A acronym “B4P” as the search item at rcsb.org. The abbreviations are: aaRS—aminoacyl tRNA synthetase; IMPDH—inositol-monophosphate dehydrogenase; tbp—to be published.

Function	Protein	Organism	Function	PDB-ID	Citation
Bacteria
Producer	Lys-aaRS	Geobacillus stearothermophilus	Synthesis of Lys-tRNAs	3A74	tbp
	LysU	E. coli	Synthesis of Lys-tRNAs	5YZX	tbp
	Propionate kinase TdcD	S. typhimurium	Anaerobic breakdown of L-threonine to propionate	2E1Z, 2E20	(Simanshu et al. 2008b)
Degrader	RppH	E. coli	AP4A hydrolysis and AP4A-decapping of mRNA	7SP3	(Levenson-Palmer et al. 2022)
	AP4A hydrolase (aq_158)	Aquifex aeolicus Vf5	AP4A degradation	3I7V	(Jeyakanthan et al. 2010)
Target	Pyrophosphatase (Family II PPase) activated by AP4A	Clostridium perfringens	Ppase activity is inhibited by AMP and activated by AP4A	3L2B	(Tuominen et al. 2010)
Target	IMPDH inhibited by AP4A	B. subtilis	NAD-dependent conversion of IMP to XMP	7OJ1	(Giammarinaro and Young et al. 2022)
Target	YxkO, role of AP4A unknown	B. subtilis	ADP/ATP-dependent NAD(P)H-hydrate dehydratation	3RQX	(Shumilin et al. 2012)
	Propionate kinase TdcD, role of AP4A unknown	S. typhimurium	Anaerobic breakdown of L-threonine to propionate	2E1Z, 2E20	(Simanshu et al. 2008b)
	tm0922, role of AP4A unknown	Thermotoga maritima	Unknown function	3RSF	(Shumilin et al. 2012)
Eukaryotes
Producer	GLYRS	Homo sapiens	Gly-aaRS	2ZT5, 2ZXF	tbp
Degrader	Apa2	Saccharomyces cerevisiae	AP4A phosphorylase	4I5V	(Hou et al. 2013)
Target	HINT1 (histidine triad nucleotide-binding protein 1), AP4A inhibits HINT1	Homo sapiens	AP4A binds HINT1, disrupts interaction with the microphthalmia-associated transcription factor (MITF) → activates transcription of genes downstream of MITF in response to immunostimulation	6J65, 6J64	(Yu et al. 2019)
Target	NPP3 Ectonucleotide phosphodiesterase/pyrophosphatase-3, role of AP4A unknown	Rattus norwegus	membrane-bound glycoprotein that regulates extracellular levels of nucleotides	6F2Y	(Döhler et al. 2018)
Target	Cytosolic 5′-Nucleotidase II, role of AP4A unknown	Homo sapiens	dephosphorylation of 6-hydroxypurine nucleoside 5′-monophosphates	2XJC	(Walldén and Nordlund 2011)
Target	Adenosine Kinase, role of AP4A unknown	Anopheles gambiae	NTP-dependent phosphorylation of adenosine into AMP	3LOO	(Cassera et al. 2011)
Target	Adenylate kinases 1,2, role of AP4A unknown	Homo sapiens	2 ADP → ATP + AMP	2C9Y, 2C95	tbp