I would like to find the protein sequence for human APOB.

I was not able to query by "APOB" so I first looked up the Entrez ID, 338.

libraryUniProt.ws)
human <- UniProt.ws(9606)

keys <- c("338")
columns <- c("SEQUENCE","UNIPROTKB","PDB")
kt <- "ENTREZ_GENE"
res <- select(human, keys, columns, kt)

This returns the main protein, but also two variants. One variant is labeled "Apolipoprotein B variant". How can I add this label so that I am able to determine the one I want.

Also, can I search "ABOB" directly rather than going through the Entrez ID? Thanks!

James MacDonald's suggestion worked for this part.

keys <- c("APOB")
columns <- c("SEQUENCE","UNIPROTKB","PDB","GENECARDS")
kt <- "GENECARDS"
res <- select(human, keys, columns, kt)

I think you can use the GENECARDS keytype:

> select(ws, "APOB", c("SEQUENCE","UNIPROTKB","PDB"), "GENECARDS")
Getting mapping data for APOB ... and ACC
Getting mapping data for P04114 ... and PDB_ID
Getting extra data for P04114
'select()' returned 1:1 mapping between keys and columns
  GENECARDS
1      APOB
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1 MDP<snip>KLAPGELTIIL
  UNIPROTKB  PDB
1    P04114 <NA>
>