extractProtPSSM {Rcpi} | R Documentation

## Compute PSSM (Position-Specific Scoring Matrix) for given protein sequence

### Description

Compute PSSM (Position-Specific Scoring Matrix) for given protein sequence

### Usage

    extractProtPSSM(seq, start.pos = 1L, end.pos = nchar(seq),
      psiblast.path = NULL, makeblastdb.path = NULL, database.path = NULL,
      iter = 5, silent = TRUE, evalue = 10L, word.size = NULL,
      gapopen = NULL, gapextend = NULL, matrix = "BLOSUM62",
      threshold = NULL, seg = "no", soft.masking = FALSE,
      culling.limit = NULL, best.hit.overhang = NULL,
      best.hit.score.edge = NULL, xdrop.ungap = NULL, xdrop.gap = NULL,
      xdrop.gap.final = NULL, window.size = NULL, gap.trigger = 22L,
      num.threads = 1L, pseudocount = 0L, inclusion.ethresh = 0.002)

### Arguments

`seq` | Character vector, as the input protein sequence.
`start.pos` | Optional integer denoting the start position of the fragment window. Default is `1`, i.e. the first amino acid of the given sequence.
`end.pos` | Optional integer denoting the end position of the fragment window. Default is `nchar(seq)`, i.e. the last amino acid of the given sequence.
`psiblast.path` | Character string indicating the path of the `psiblast` program. If NCBI Blast+ was previously installed in the operation system, the path will be automatically detected.
`makeblastdb.path` | Character string indicating the path of the `makeblastdb` program. If NCBI Blast+ was previously installed in the system, the path will be automatically detected.
`database.path` | Character string indicating the path of a reference database (a FASTA file).
`iter` | Number of iterations to perform for PSI-Blast.
`silent` | Logical. Whether the PSI-Blast running output should be shown or not (May not work on some Windows versions and PSI-Blast versions), default is `TRUE`.
`evalue` | Expectation value (E) threshold for saving hits. Default is `10`.
`word.size` | Word size for wordfinder algorithm. An integer >= 2.
`gapopen` | Integer. Cost to open a gap.
`gapextend` | Integer. Cost to extend a gap.
`matrix` | Character string. The scoring matrix name (default is `'BLOSUM62'`).
`threshold` | Minimum word score such that the word is added to the BLAST lookup table. A real value >= 0.
`seg` | Character string. Filter query sequence with SEG (`'yes'`, `'window locut hicut'`, or `'no'` to disable) Default is `'no'`.
`soft.masking` | Logical. Apply filtering locations as soft masks? Default is `FALSE`.
`culling.limit` | An integer >= 0. If the query range of a hit is enveloped by that of at least this many higher-scoring hits, delete the hit. Incompatible with `best.hit.overhang` and `best_hit_score_edge`.
`best.hit.overhang` | Best Hit algorithm overhang value (A real value >= 0 and =< 0.5, recommended value: 0.1). Incompatible with `culling_limit`.
`best.hit.score.edge` | Best Hit algorithm score edge value (A real value >=0 and =< 0.5, recommended value: 0.1). Incompatible with `culling_limit`.
`xdrop.ungap` | X-dropoff value (in bits) for ungapped extensions.
`xdrop.gap` | X-dropoff value (in bits) for preliminary gapped extensions.
`xdrop.gap.final` | X-dropoff value (in bits) for final gapped alignment.
`window.size` | An integer >= 0. Multiple hits window size, To specify 1-hit algorithm, use `0`.
`gap.trigger` | Number of bits to trigger gapping. Default is `22`.
`num.threads` | Integer. Number of threads (CPUs) to use in the BLAST search. Default is `1`.
`pseudocount` | Integer. Pseudo-count value used when constructing PSSM. Default is `0`.
`inclusion.ethresh` | E-value inclusion threshold for pairwise alignments. Default is `0.002`.

### Details

This function calculates the PSSM (Position-Specific Scoring Matrix) derived by PSI-Blast for given protein sequence or peptides. For given protein sequences or peptides, PSSM represents the log-likelihood of the substitution of the 20 types of amino acids at that position in the sequence. Note that the output value is not normalized.

### Value

The original PSSM, a numeric matrix which has `end.pos - start.pos + 1` columns and `20` named rows.

### Note

The function requires the `makeblastdb` and `psiblast` programs to be properly installed in the operation system or their paths provided.

The two command-line programs are included in the NCBI-BLAST+ software package. To install NCBI Blast+, just open the NCBI FTP site using web browser or FTP software: ftp://anonymous@ftp.ncbi.nlm.nih.gov:21/blast/executables/blast+/LATEST/ then download the executable version of BLAST+ according to your operation system, and compile or install the downloaded source code or executable program.

Ubuntu/Debian users can directly use the command `sudo apt-get install ncbi-blast+` to install NCBI Blast+. For OS X users, download `ncbi-blast- ... .dmg` then install. For Windows users, download `ncbi-blast- ... .exe` then install.

### Author(s)

Nan Xiao <https://nanx.me>

### References

Altschul, Stephen F., et al. "Gapped BLAST and PSI-BLAST: a new generation of protein database search programs." Nucleic acids research 25.17 (1997): 3389–3402.

Ye, Xugang, Guoli Wang, and Stephen F. Altschul. "An assessment of substitution scores for protein profile-profile comparison." Bioinformatics 27.24 (2011): 3356–3363.

Rangwala, Huzefa, and George Karypis. "Profile-based direct kernels for remote homology detection and fold recognition." Bioinformatics 21.23 (2005): 4239–4247.

### See Also

extractProtPSSMFeature extractProtPSSMAcc

### Examples

    x = readFASTA(system.file('protseq/P00750.fasta', package = 'Rcpi'))[[1]]

    dbpath = tempfile('tempdb', fileext = '.fasta')
    invisible(file.copy(from = system.file('protseq/Plasminogen.fasta', package = 'Rcpi'), to = dbpath))
    pssmmat = extractProtPSSM(seq = x, database.path = dbpath)
    dim(pssmmat)  # 20 x 562 (P00750: length 562, 20 Amino Acids)

[Package Rcpi version 1.16.2 Index]