Table I.

Differences Between Thermophilic and Mesophilic Membrane Protein Structures

	Transmembrane			Soluble			P-value of Mann-Whitney U-Test
	Average and standard errora			Average and standard errora			Transmembrane		Soluble
Property	Thermophile	Mesophile	Paired differenceb	Thermophile	Mesophile	Paired differenceb	Unpaired	Paired	Unpaired	Paired
Burial (fractional side-chain buried)	0.780 ± 0.027	0.733 ± 0.012	0.054 ± 0.045	0.672 ± 0.021	0.661 ± 0.008	0.004 ± 0.025	0.026*	0.133	0.124	0.496
Packing	0.719 ± 0.006	0.727 ± 0.002	−0.002 ± 0.012	0.718 ± 0.004	0.717 ± 0.002	0.003 ± 0.004	0.063	0.433	0.296	0.234
Surface loop length (number of residues)	N/A			19.126 ± 0.735	19.189 ± 0.747	−0.063 ± 0.203				0.491
Helix length (number of residues)	25.627 ± 0.723	26.969 ± 0.789	0.404 ± 1.074	N/A			0.269	0.304
Kinks (number per TM-helix)	0.070 ± 0.008	0.073 ± 0.004	−0.011 ± 0.009				0.455	0.190
Interhelical H-bonds (number per residue)	0.102 ± 0.020	0.115 ± 0.008	−0.028±0.025				0.205	0.160
Hydrophobicity	0.126 ± 0.024	0.220 ± 0.015	0.039 ± 0.034				0.005*	0.336

^aFor unpaired structure or direct homolog data sets.

^bMean difference (thermophiles–mesophiles) with standard error (A paired difference of 0 indicates no difference between paired thermophiles and mesophiles).

^*Statistically significant (P < 0.05).