Table 3. Similarities and differences in expression profiles, amino acid sequences and common motifs of neuronal UCPs^*.

Conserved/semi-conserved sequences
	UCP2	UCP4	UCP5
MCF conserved sequences [48]	Px[D/E]xx[K/R]x[R/K]-20-30 aa-[D/E]Gxxxx[W/Y/F]-[K/R]G
Inter-helical association motif [46]	GxxxG
Proton transport residue [54]	Asp28	Glu34	Glu55
Charged residues in chloride-binding region [55]	Asp35, Lys38, Arg88, Asp138, Lys141, Lys239 and Asp236	Asp41, Lys44, Arg97, Asp149, Lys152, Lys253 and Asp250	Asp60, Lys66, Arg113, Asp163, Lys166, Lys260 and Asp257
PN-binding residues [9]	Arg88, Arg185, Arg279	Arg97, Arg199, Arg299	Arg113, Arg206, Arg305
Unique biochemical/biophysical properties
	UCP2	UCP4	UCP5
Expression profile	Expression in various tissues and organs (brain, muscle, liver, heart, kidney, pancreas)	Primarily expressed in the brain and the CNS (neurons, astrocytes, Purkinje cells)	Primarily expressed in the brain and to a lesser extent in testis, uterus, kidney, lung, stomach
Sequence identity to UCP1	59%	34%	30%
Proton transport rate (μmol·min−1·mg·protein−1)	∼2–5 (strongest activator: AA)	∼1–4 (strongest activator: OA)	∼2–6 (strongest activator: OA)
Chloride transport rate (μmol·min−1·mg·protein−1)	∼1	∼0.5	∼0.5
Interaction with CL [11]	CL induced higher UCP2-mediated H+ flux	CL had no effect on UCP4-mediated H+ flux	CL induced higher UCP5-mediated H+ flux

*Conserved/semi-conserved amino acid sequences were extracted from the multiple sequence alignment of neuronal UCPs with other UCPs and AACs. The amino acid sequence alignment of AACs and human UCP homologues were done using the Clustal Omega [26] program and viewed with Jalview [27].