The Jackprot Simulation Couples Mutation Rate with Natural Selection to Illustrate How Protein Evolution Is Not Random

Table 2 KcsA amino acid site specificity for plasma membrane hydrophobicity and hydrophilicity

Membrane region^a aa sequence	Amino acid polarity				Total	Statistical difference binomial-test p value
	No. polar (P)	Electrically charged (EC)		No. non-polar (NP)	P + EC vs. NP
	No. polar (P)	No. acidic	No. basic	No. non-polar (NP)	P + EC vs. NP
Pre-M1 segment MPPMLSGLLARLVKLLLGRHGSALH	5	0	5	15	10/15	n.s.
M1 WRAAGAATVLLVIVLLAGSYLAVLA	5	0	1	19	6/19	0.014
Turret region ERGAPGAQLI	3	1	1	5	5/5	n.s.
Pore-forming loop TYPRALWWSVETA	4	1	1	7	6/7	n.s.
Signature sequence TTVGYG	5	0	0	1	5/1	N/A
Extended region DLYPVTL	2	1	0	4	3/4	N/A
M2 WGRLVAVVVMVAGITSFGLVTAALA	6	0	1	18	7/18	0.04
Post-M2 segment TWFVGREQERRGHFVRHSEKAAEE AYTRTTRALHERFDRLERMLDDNRR	10	10	15	14	35/14	0.003
Total	40	13	24	83	77/83	n.s.

Polar (P) plus electrically charged (EC) versus non-polar (NP) amino acids are unequally distributed across the plasma membrane (Chi-square = 21.20; df = 5; p ≤ 0.001; P + EC vs. NP for the signature sequence and extended region were excluded from the Chi-square analysis because their expected values in the contingency table were less than five). Note how NP residues are significantly more frequent than P + EC amino acids in the hydrophobic regions M1 and M2, while P + EC residues in the post-M2 segment are significantly more frequent inside the cytoplasmic environment than NP amino acids. Residue regions correspond to Fig. 1
^aMembrane region after Shealy et al. 2003; protein sequence available at NCBI (GenBank Z37969; Swiss-Prot P0A334)

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